Full text of "The Dorling Kindersley Science Encyclopedia"

See other formats

A milestone in scientific learning

A comprehensive reference work

Packed with up-to-date information, The Science Encyclopedia
explains the principles of science in a lively and exciting way.

The scope of subjects covered is immense - from atoms to
lasers, from acids to speedometers, from marsupials to
magnets. More than 280 major entries cover key subjects
such as evolution and energy, polymers and pollution,
while a further 1.900 subentries include biographies of great
scientists and inventors, timecharts detailing landmarks in
science, and factboxes on subjects of general scientific interest

Organized for ease of use

The Science Encyclopedia has been designed to make science
accessible. Qearh organized into 12 thematic sections, the book
reflects the integration of science and technology into our
evemiav lives and forges links between different areas of science
that relv on common principles. So, for example, entries on
reflection, refraction, and electromagnetic spectrum are found
together in the section on Sound and Light, while photosynthesis,
genetics, and digestion are located in How Living Things Work.

Richly illustrated and easy to read

Over 2,500 full-colour photographs, detailed artworks, and informative
maps and charts make The Science Encyclopedia an enticing reference
book. Many of the photographs have been specially commissioned
to demonstrate scientific processes or experiments, while the
cutaway artworks explain the inner workings of a host of objects,
from human cells to catalytic converters, from air conditioners
to paper mills. These spectacular illustrations are brought to
life by a lively and informative text compiled by an impressive
team of authors, editors, and specialist consultants from a wide
range of scientific disciplines.

£29.95

The Dorling Kindersley

SCIENCE

Encyclopedia

DORLING KINDERSLEY
London New York Stuttgart

A DORLING KINDERSLEY BOOK

Senior Editor Susan McKeever Senior Art Editor Martyn Foote

Editors

Caroline Beattie, Helen Dowling, Linda Martin,

Mina Patria, Louise Pritchard, Jackie Wilson

Art Editors

Alexandra Brown, Wayne Holder, Marcus James, Rebecca Johns,
Carole Orbell, Tina Robinson, Simon Yeomans, Dominic Zwemmer

Managing Editor Sophie Mitchell Managing Art Editor Miranda Kennedy
Picture Research Lorna Ainger, Caroline Brooke, Anne Lyons,
Catherine O’Rourke, Christine Rista
Production Louise Barratt, Ruth Cobb

Editorial consultants

Heather Couper BSc, FRAS, Hon. D. Litt
Nigel Henbest BSc, MSc, FRAS

Contributors

David Burnie BSc; Karen Davies BSc PGCE; Dougal Dixon BSc PhD; David Glover BSc PhD;
John Gribbin MSc PhD; Mary Gribbin BA; Ian Harrison BSc PhD MBA; Robin Kerrod FRAS;
Peter Lafferty BSc MSc PGCE; Peter Riley BSc C. Biol PGCE;

Carole Stott BA FRAS; Barbara Taylor BSc; Keith Wicks

Educational consultants

David Evans BSc, C. Biol, M. I. Biol
Kimi Hosoume BA

History of science consultant

Patricia Fara BSc, MSc

Natural history consultant

Steve Parker BSc

First published in Great Britain in 1993
by Dorling Kindersley Limited
9 Henrietta Street, Covent Garden, London WC2E 8PS
Reprinted twice with revisions 1994
Reprinted 1995, 1996 (twice)

Revised edition 1997
468 10 9753

This edition published 1998 for Covent Garden Books

Visit us on the World Wide Web at
http://www.dk.com

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted by any means,
electronic, photocopying, recording, or otherwise, without the prior permission of the copyright owner.

A CIP catalogue record for this book is available from the British Library

ISBN 1-85605-465-9

Colour reproduction by Colourscan, Singapore
Printed and bound in Italy by A. Mondadori Editore, Verona

CONTENTS

8-9

HOW TO USE
THIS BOOK

TIME CHARTS

42 Nitrogen

43 Phosphorus

44 Oxygen

45 Sulphur

46 Halogens

47 Hydrogen

48 Noble gases

10 Discovering Matter

11 Discovering Energy

12 Discovering Earth and Space

13 Discovering Living Things

14-15

HOW SCIENTISTS
WORK

SAFETY CODE

MATTER

18 States of matter
20 Changes of state
22 Properties of matter
24 Atomic structure
26 Radioactivity
28 Bonding

30 Crystals

31 Elements

32 Periodic table

34 Alkali metals

35 Alkaline-earth metals

36 Transition metals

38 Poor metals

39 Semimetals

40 Carbon

41 Organic chemistry

REACTIONS

50 Kinetic theory

51 Behaviour of gases

52 Chemical reactions

53 Describing reactions

54 Reversible reactions

55 Rates of reaction

56 Catalysts

58 Compounds and mixtures

60 Solutions

61 Separating mixtures

62 Chemical analysis

64 Oxidation and reduction

66 Reactivity series

67 Electrolysis

68 Acids

70 Alkalis and bases

72 Measuring acidity

73 Salts

74 Chemistry of air

75 Chemistry of water

76 Chemistry of the body
78 Chemistry of food

80 Fermentation

MATERIALS

82 Chemical industry

83 Water industry

84 Iron and steel

86 Copper

87 Aluminium

88 Alloys

89 Sulphuric acid

90 Ammonia

91 Chemistry in farming

92 Food industry

94 Alkali industry

95 Soaps and detergents

96 Coal products

97 Gas products

98 Oil products
100 Polymers

102 Dyes and pigments

103 C Cosmetics

104 Chemistry in medicine

106 Adhesives

107 Fibres

108 Paper

109 C Ceramics

110 Glass

111 Material design

112 Industrial pollution

113

FORCES AND
ENERGY

114 Forces

116 C Combining forces

117 Balanced forces

118 Speed

119 Acceleration

120 Forces and motion

121 Friction

122 Gravity

123 Measuring forces

124 Turning forces

125 Circular motion

126 Vibrations

127 Pressure

128 Forces in fluids

129 Floating and sinking

130 Machines

132 Work and Energy
134 Energy sources
136 Nuclear energy
138 Energy conversion
140 Heat

142 Heat transfer

143 Engines

146 Static electricity
148 Current electricity
150 Cells and batteries
152 Circuits
154 Magnetism
156 Electromagnetism

158 Electric motors

159 Generators

160 Electricity supply

161 Electricity in the home

162 Telecommunications
164 Radio

166 Television

168 Electronic components

170 Integrated circuits

172 Calculators

173 Computers

175 Using computers

176 Robots

178 Sound

180 Measuring sound

181 Loudness

182 Making and hearing
sound

184 Reflection and
absorption
186 Musical sounds

188 Sound recording

189 Electronic sounds

190 Light

192 Electromagnetic
spectrum

193 Sources of light

194 Reflection

196 Refraction

197 Lenses

198 Optical instruments

199 Lasers

200 Light and matter

201 Shadows

202 Colour

203 Colour subtraction

204 Vision

206 Photography
208 Cinema

209

EARTH

210 Formation of the Earth
212 Structure of the Earth
214 Moving continents

177

SOUND AND
LIGHT

ELECTRICITY AND
MAGNETISM

216 Volcanoes

218 Mountain building

220 Earthquakes

221 Rocks and minerals

222 Igneous rocks

223 Sedimentary rocks

224 Metamorphic rocks

225 Fossils

226 Record in the rocks
228 Ice and glaciers

230 Weathering and erosion

232 Soils

233 Rivers

234 Seas and oceans

235 Waves, tides and
currents

236 Shoreline

238 Coal

239 Oil and gas

240 Mapping the Earth

Owe

241

WEATHER

242 Sunshine

243 Seasons

244 Climates

246 Changing climates
248 Atmosphere

250 Air pressure

251 Temperature

252 Humidity

253 Fronts

254 Winds

256 Wind strength

257 Thunder and lightning

258 Hurricanes

259 Tornadoes

260 Clouds

262 Formation of clouds

263 Fog, mist, and smog

264 Rain

266 Snow

267 Hail

268 Frost, dew, and ice

269 Special effects

270 Forecasting

272 Weather watching

CONTENTS

273

SPACE

274 Universe

275 Origin of the Universe

276 Galaxies
278 Stars

280 Life cycle of stars

282 Constellations

283 Solar system

284 Sun

286 Mercury and Venus

287 Earth

288 Moon

289 Mars

290 Jupiter

291 Saturn

292 Uranus

293 Neptune and Pluto

294 Asteroids

295 Comets and meteors

296 Study of astronomy

297 Telescopes on Earth

298 Telescopes in space

299 Rockets

300 Satellites

301 Space probes

302 Humans in space
304 Space stations

LIVING THINGS

306 What is life?

307 How life began

308 Evolution

309 How evolution works

310 Classifying living things

312 Viruses

313 Bacteria

314 Single-celled organisms

315 Fungi

316 Plants without flowers

317 Conifers

318 Flowering plants

320 Jellyfish, anemones, and
corals

321 Worms

322 Arthropods

324 Molluscs

325 Starfish and sea squirts

326 Fish

328 Amphibians
330 Reptiles
332 Birds
334 Mammals
336 Primates

337

HOW LIVING
THINGS WORK

338 Cells

340 Photosynthesis

341 Transport in plants

342 Nutrition

343 Feeding

344 Teeth and jaws

345 Digestion

346 Cellular respiration

347 Breathing

348 Blood

349 Circulation

350 Internal
environment

352 Skeletons

354 Skin

355 Muscles

356 Movement
358 Senses

360 Nerves

361 Brains

362 Growth and
development

364 Genetics

366 Asexual reproduction

367 Sexual reproduction

368 Human reproduction

369

ECOLOGY

370 The biosphere

372 Cycles in the biosphere

374 People and planet

376 Wastes and recycling

377 Food chains and webs

378 Animal groups

379 Partnerships

380 Colour and camouflage

381 Migration and
hibernation

382 Polar and Tundra lands

384 Mountains

385 Seashores

386 Oceans

388 Rivers and lakes

389 Wetlands

390 Deserts
392 Grasslands

394 Tropical rainforests

396 Temperate forests

397 Towns and cities

398 Wildlife in danger
400 Conservation

401-425

FACT FINDER
SECTION

426-433

GLOSSARY

434-445

INDEX

446

ACKNOWLEDGMENTS

Chemistry of Food or Reptiles. To find
an entry, look on the contents pages,
where the heading of each page is
listed, or turn to the index, which tells
you which pages contain information
on the subject you are looking up.

These pages show you how to use The
Dorling Kindersley Science Encyclopedia. The
enyclopedia is divided into 12 thematic
sections, such as Reactions and Living
Things. Within each section are main
entries on the subject, such as the

The 12-page index is at the back
of The Science Encyclopedia. The
numbers refer to page numbers.

The page number in normal
type gives general
\ references within The
\ Science Encyclopedia.

I The page number in bold
I type gives the main entry.

INDEX

mimals

The

index lists all the
subjects in The Science
Encyclopedia, with the
pages they appear on.

biosphere cycles 3^
brain 361
breathing 347
burrowing 393
carbon cycle 41
cells 337, 338
classification 310-11

421 _ y

:climate and 142/

Each main entry is
either one or two
pages long.

The

contents
pages list each
page subject
under its thematic
section head.

SCIENCE THEMES
Information in the encyclopedia
is arranged in a thematic way.
Each entry gives detailed
information on one topic,
making it ideal for project work.
Reading other pages in the same
section enables you to explore
and understand the subject fully.
This page on Chemical Analysis
is from the Reactions section.

The words and pictures describe
subjects such as Chromatography
and Flame Tests in a clear and
exciting way.

CHEMICAL ANALYSIS

CONTENTS

MATERIALS

11 ME UI ARTS

Atomic Structure
tells you what
atoms are made of.

Find out more

f TIME CHARTS
There are four different time charts
at the front of The Science Encyclopedia.
Each one has a theme: Matter, Energy,
Earth and Space, and Living Things.
The time charts trace the development
of different branches of science, from
the earliest times to the present day.

Atomic structure

Atomic structure p.24
Compounds and
mixtures P.58
Separating mix tures p.61
Sources of light p.193
Genetics p.364
Fa Cl FINDER P. 4 0 4

Sources of Light explains
why atoms give out light
when heated - a method
of identifying an element.

FIND OUT MORE
There is a Find out more box in the
bottom right-hand corner of each
entry page. This box lists other
pages in The Science Encyclopedia
where you can find out more about
your subject. For example, the Find
out more box on the Chemical
Analysis page lists six related
entries and their page numbers.

Sources ok light

DISCOVERING MATTER

Genetics tells you how
a chemical code in
DNA makes each
being unique.

The Find out more
box on Sources of
Light leads you to four
related entries: Noble
Gases, Chemical
Reactions, Electricity
Supply, and Colour.

HOW TO USE THIS BOOK

Cutaway

illustrations

Some pages have
illustrations that reveal
the insides of objects
and living things.

This illustration of a
toadstool shows
what it is made up
of and how it works.

MAIN ENTRIES

The information on each page is presented in away that
makes it easy to understand what is going on. Start
reading at the introduction, move on to the sub-entries
and then read the captions and annotations.

Introduction

Each main entry starts with an
introduction that provides a clear
explanation of the subject. After
reading this, you should have a good
idea of what the page is all about. s

Entry heading

This big heading at
the top of the page
describes a main entry.

Sub-entry

A sub-entry is under the second-largest
heading on the page. It examines aspects
of the main entry in detail. For example,
the sub-entries on Kinetic Theory are
about diffusion and expansion, both
important examples of kinetic theory.

Photographs

All the pages in The Science
Encyclopedia have photographs. This
photograph of bromine diffusion was
specially taken in a studio, so that you
can see exactly what really happens.

Special information boxes

On some pages, you will find information
boxes, which highlight particular aspects
of a main entry. This box tells you about
Brownian motion, which can be
explained by kinetic theory.

Running head

This reminds you which
section you are in. This
entry on Kinetic Theory is in
the Reactions section.

Captions and annotations

Every illustration has a caption. They
often have annotations (in italics) as
well.These point out important details
within an illustration or photograph.

Biographies

Many pages contain biographical details
of notable scientists and inventors.
Biographies tell you about the life of the
scientist or inventor, when they lived,
and what they did.

Maps

The maps in The Science Encyclopedia
give at-a-glance geographical
information. For example, this map
appears on a page about mountain
ecosystems. It shows where the main
mountain ranges of the world are.

Date boxes

Many pages have a date box. These
give landmarks of achievement in
date order. This date box appears on
a page called Optical Instruments. It
gives the dates of when the most
important telescopes were built.

Diffusion

se the molecules in a gas
fast, gases will spread out and
space as possible. The way
in which gas molecules spread out is called
diffusion, and it is the reason why smells
travel so quickly. For example, when bread
is baking in the oven, the smell of cooking
diffuses through the whole house.

Expansion

If an object, like this
thermometer, is heated, its
j,IK t particles start to move faster
; :5- and take up extra space. It is
jj: •» said to expand. This is why
«•:; *«• railway lines include small
£;j gaps that the metal can
r* , expand into in hot weather.

I .iquids expand about ten
limes more than solids.
Gases expand about 100
than liquids.

hi diffuse

BROWNIAN MOTION

In 1827, the Scottish botanist
Robert Brown was surprised to see
that some pollen grains in water
were haphazardly bouncing about.
The great scientist Albert Einstein
explained this movement eighty
years later by using the kinetic
theory. The pollen grains are
being constantly bombarded by
, unseen water molecules. Thi
type of movement is now called

Illustrations

Most pages in The Science
Encyclopedia contain clear, detailed
illustrations that help you to
understand scientific concepts.

Kinetic theory

TiAVE YOU EVER WONDERED why you can smell food cooking?
TheYcason is that tiny gas molecules from hot food whirl through
the air ahd some reach your nose. Although it is hard to believe,
the atoms ahtfmolecules that make up everything we sec arc
constantly movrhg. As the temperature rises, the particles move
faster, and so they take up more space. This is the kinetic theory
of matter. The word “kinetic” means moving. Not all particles can
move in the same way. In solids, the particles are closely packed
together and can only move by vibrating or shaking. In liquids, the
particles arc still close, but they can move more freely. In a
gas, the particles are widely spaced and move very fast.

IMPORTANT
TELESCOPES

1789 William Herschelj
England, 1.23 m (4 It ) diamej
1845 Lord Rosse teU
Ireland, 1.83 m (6jf
1917 Mount WU
California, USJg 2.54
diameter.

1948 Hale Reflector, Palomar,
California, USA, o m (16 ft)
diamel^iC /'V
1976 XiountZ^emirodriki
telescope, <5lS, 6 m (19.5 ft)
diajtneier.

1992 Keek telescope, Hawaii,
TO lilt33 ft) diameter.

FACT FINDER

The Fact finder pages at the back of The Science Encyclopedia
are packed with useful charts, facts, and figures on all the
topics in the encyclopedia. These pages are from the
Reactions section.

A chart shows you the reactivity series,
and illustrates what happens to
different metals when they are mixed
with various substances.

The different laws
for identifying
gases are
explained.

A table shows you
what endings and
prefixes of chemical
names mean.

The chemical equipment you might use in a
science laboratory is illustrated and explained.

ABBREVIATIONS

Some words are abbreviated (shortened) in
r The Science Encyclopedia. The following list
explains what the abbreviations stand for:

°C = degrees Celsius

°F = degrees Fahrenheit

mm - millimetre

cm = centimetre

m = metre

km = kilometre

sq km = square kilometre

km/h = kilometres per hour

g = gram

kg = kilogram

1 = litre

in = inch

ft = foot

yd = yard

mph - miles per hour
oz = ounce
lb = pound

c. before a date = about
B.c. = before Christ

A.d. = anno Domini, after the birth of Christ

HISTORY OF SCIENCE • MATTER

DISCOVERING MATTER

400 b.c.

The Greeks Democritus
and Epicurus teach A
that matter consists
of small, hard,
invisible particles
called atoms.

For hundreds of years,
people believe Aristotle’s
theory that there are four
basic elements - earth,
fire, air and water.

300 b.c.

Greek philosophers Plato and
Aristotle believe that you can always
go on cutting matter into smaller
and smaller
pieces. '

Plato considered these solids represented the
atoms of the four elements: earth,
air, fire, and water. ^—

Skilled craftworkers
such as miners, cloth dyers
and pottery makers are the
experts in manufacturing
techniques.

Democritus

1661

Irishman Robert Boyle suggests
that small moving particles can
explain chemical reactions better
than Aristotle’s ^—■

four elements.

Gas molecules
diffuse (spread
out) into the air
in a gas jar.

Antoine Lavoisier
(1743-94) uses
oxygen instead of
phlogiston to explain
burning and other
chemical changes.

Steel component '
v of a steam-
powered ship.

Chemical j
processes are
explained by I
phlogiston, an
invisible
substance
released into the air
during burning.

^ Englishman

- , Sir Isaac

Newton
(1643-1727)
describes how
minute particles can
attract and repel
each other.

Researchers study
heat and investigate
newly discovered
gases such as
carbon dioxide.

Sodium '■ J
and chlorine '
atoms join
together to form
sodium chloride.

Cheap, high- ^
quality iron is
used to make steel.

1808

English chemist John £
Dalton introduces Aj
modern chemical ideas^
of elements and^
compounds made from
atoms and molecules.

Coal consists,
mainly of A
carbon. /jR

f 1830

* German chemists
f focus on carbon as
the basis of the
organic chemistry of
living beings.

Internal M
combustion A
engines, using ™
either gas or
petrol, are invented.

In 1913 atoms shown to
contain a small nucleus,
surrounded by even i
smaller electrons. J

1897

British physicist
J.J. Thomson’s
discovery of electrons ^
suggests that atoms are
not the smallest particles.

Artificial jc
pigments and ig
dyes are added ^
to ink to give it \
colour.

Important new chemical
industries, including
synthetic drugs and
dyes, are developed in
Germany.

Russian Dmitri Mendeleyev devises the
Periodic Table, which classifies elements
into similar
groups by their
atomic weight.

- Potentially harmful
X-rays are modified to
provide beneficial medical
information. They enable
doctors to see the body
beneath the skin.

The Periodic Table

1920

Telephones are
mass-produced from
Bakelite, a synthetic
plastic. The plastic
industry begins to
grow into one of the
world’s largest.

660

666

6660

0600

1939-45

During the Second World
War, research focuses on
the atomic bomb and the
life-saving drug penicillin.

. 7 Scientists explore
inside the central
nucleus of atoms. Even
smaller particles, protons
and neutrons, are discovered.

Many objects are made
from plastic. —-

Cheap
clothes are
made from
new
artificial
fabrics such
as nylon.

Physicists

Quarks are discovered
inside protons and
neutrons.

continue to discover
smaller and smaller subatomic
Heated nylon particles called quarks.

polymer is cooled to
form solid threads.

These are spun and

Scientists are

HISTORY OF SCIENCE • ENERGY

DISCOVERING ENERGY

Early civilizations rely on
wind and muscle power for
travelling and building, and
use wood for
* ^ m. j * heat.

The Greek mathematician Archimedes
establishes the principles of
| mechanics and invents many
important devices.

For hundreds of years, ideas
are dominated by the work of
the Greek philosopher
Aristotle.

The Italian physicist and
astronomer Galileo insists on using
experiments and mathematics for
i exploring nature.

Archimedes’ screw

Apparatus to
show Galileo’s
projectile
experiment.

—- 1687

--" Isaac Newton

publishes his theory of gravity, a
single mathematical law describing
the movement of distant planets
as well as objects on Earth.

For many years, argument
rages between supporters
of Newton’s idea that light
consists of tiny particles
and Dutch physicist
Huygen’s suggestion that
light is made from waves.

1745

The invention of the
Leyden jar, which can
store static electricity,
enables new electrical
experiments to be
carried out.

1760 " 70 "S*..

The earliest *^5

steam engines J

replace horses for
pumping water out of tin
mines. Steam engines
are later developed into
locomotives.

In Italy, Alessandro Volta
invents the battery, the
first source of current
v electricity.^ — ^——

— Using advanced

mathematical techniques and
delicate experiments,
French researchers
establish the wave
V theory of light.

1820-31 ^

Ear 5 English scientist

Hr Michael Faraday H

■Mi uses attracting and VL
B repelling magnetic

forces as a basis for the ^
dynamo, crucial for supplying
domestic and industrial electricity.

Steam engines power
the new factories and trains,
making Britain the world’s first
industrialized nation.

1888

German
physicist
Heinrich Hertz
creates radio
waves in his
laboratory, a
discovery vital
i for science.

As machines become
. more important,

% physicists and
Ik engineers study the
ip relationships
T between heat,

| power, and work.

Public gas and
electricity
{networks start to
ftransform
| industry as well
as people’s daily
lives.

1915

German-born Albert Einstein
revolutionizes our views of the
Universe by introducing his
general relativity theory.

Phonographs and
moving films are
invented: the
entertainment
industry is born.

James Joule (1818-89)
realizes that work
produces heat.

New theories
called quantum
mechanics
explain that
light is a
stream of tiny
photons that
act as waves
and particles.

In 1919 Einstein
proposes that light is
bent by gravity.

Light from a star is
bent by the Surr^

Scientists
f learn more
about

} radioactivity as
'they investigate the

N internal structure
, of the atomic
* nucleus.

The world is

f shocked by the
I destructive power ^ ^

of the atomic bomb
V as two American H*
\bombs fall on Japan.

New electricity generating stations
harness nuclear energy for more
peaceful purposes.

The powerful
beams of light
produced by
lasers soon
find many

f uses in
physics,
industry,

and medicine.

-A Travelling speeds increase as
Jfr Americans land on
V the moon and - ,

Concorde completes its HL \*
maiden flight in 1969.

^^ Ecologists become

increasingly concerned
z&bout using safer sources of
power which will not damage
the environment.

Scientists
continue to
investigate
whether all the
galaxies in the
Universe are
ruled by the
same laws of
physics.

1979

Studying the Universe’s four forces,
physicists successfully link the
Sfck electromagnetic and weak

.^^^^^^^luclear forces.

HISTORY OF SCIENCE • EARTH AND SPACE

DISCOVERING EARTH AND SPACE

Early civilizations have differing ideas
about the Universe. Hindus believe
that the Earth is supported by four
elephants on top of a giant turtle.

Most Ancient Greek
philosophers believe
that the Earth is
stationary at the
centre of the Universe.

The Ancient Greeks devised
elaborate maps of the sky based
on their belief of mythological
creatures.

^ 1543

_—— The Polish

-— astronomer Copernicus

suggests that the behaviour of the
heavenly bodies could be better explained
if the Earth moved round the Sun.

Replica of Galileo’s two-
lens telescope

Galileo agrees with Copernican
theories and uses a telescope to
explore the Moon and the
planets.

— 1781

The British astronomer
William Herschel maps
the stars and discovers
a new planet called J

Uranus. ;

Isaac Newton's
concept of a
Sun-centred
planetary
system held
together by
gravity becomes
more popular.

New and more
accurate

mru ~ z. instruments

"" enable people to

record and collect information
about the earth’s atmosphere. This
new science is called meteorology.

As explorers like James
Cook undertake long scientific
expeditions, maps improve
and information is gathered
about many plants, animals
and

societies.

Page from
Herschel’s diary

H.M.S. Endeavour

A Newton meter

As European powers
expand their empires,
extensive projects are
launched to map and
measure the world.

^—-— The British

—— geologist Charles Lyell

suggests that the Earth has been
gradually changing over a long
period of time.

A visual history of
the Universe

1896

The French physicist
Henri Becquerel
discovers radioactivity,
which can measure the.
age of fossils. ^—■"

^ 1908

—--- An enormous new

telescope is built at
Mount Wilson Observatory
in California, United States.

1880s

Most scientists
believe that light and
electricity are
transmitted through
an invisible medium
called the aether
surrounding the Earth.

Scientists
become
increasingly
confident that
their picture of
the Universe
is complete.

The gas helium, one of the
Earth’s lightest elements, is
first seen in the spectrum of
the Sun.

Fraunhofer lines in the Sun’s 1
spectrum show which elements are
present in the Sun’s atmosphere.

Although ridiculed, ^3SS£-
the German
geophysicist 1

Alfred Wegener
keeps finding
evidence to support

his novel ideas of
continental drift.

A 1935

H Knowledge
■ of the
Hr Universe
continues to
grow, as Pluto
is discovered and other
galaxies are studied.

Over millions of
years, continents
drift farther apart.

Pluto with
its moon,
Charon.

Aa Radiotelescopes
dJ? enable the distant
Universe to be
surveyed. Scientists
* discuss theories
about its creation.

’Satellite launched
far into space

American and British scientists take
measurements which confirm the
revolutionary t heo ries of continental
A drift and plate
tectonics.

The Russians and
the Americans
launch manned
spacecraft to explore
the Moon and send

probes far out
If into space.

Scientists develop complex
theories that describe the creation
of the Universe in a single event
called the Big Bang.

Weather
mk> forecasting
” becomes far more
accurate with the
assistance of powerful
computers and
satellites orbiting
round the
Earth.

The Universe is portrayed by
scientists as a huge “bubble”,
expanding from a small point,
where the Big Bang occurred.

An Apollo lunar
module departing
from the surface of
the Moon ini969.

HISTORY OF SCIENCE • LIVING THINGS

DISCOVERING LIVING THINGS

The Greek philosopher Aristotle
teaches the importance of
carefully studying and
classifying animals.

Early chemists known as
‘alchemists” attempt to turn
ordinary substances into
gold. Experiments with
medical cures are also
carried out.

Early Egyptian
civilizations believe that
gods linked with plants
and animals can
influence their lives.

A 14th century manuscript
showing an alchemist at work

The Italian
Andreas Vesalius
(1514-64) dissects
dead bodies to find out
how human anatomy
wqrjsi-

The Ancient Egyptian
Goddess Bastet - a cat.

1628

In England, William
Harvey describes how the
heart continually pumps
blood around the body.

Chart showing how the
Roman snail (Helix
pomatia) is

classified. S'),

The French naturalist Georges-Louis
Buffon (1707-88) suggests that living
things might have been slowly
changing since the Earth was created.

As instruments
improve, the
W microscopic
^ structure of a
wide variety of
plants and animals
is examined in finer
detail.

1749

The Swedish botanist Carl
Linnaeus invents his
\ influential system for
classifying plants and
animals using two
^9$ Latin names.

- The

—" ’ existence of new

fossils allows Georges Cuvier
to prove that species can
become extinct
and be

■¥i , ufl created.

lean Lamarck’s theory that animals
r pass on environmental
pit adaptations to their

-% offspring is influential
~ well into the 20th
jffmU century.

Making detailed

microscopic 4;

examinations, 41
r German
* & biologists put
forward new
theories about the
^ development of
embryoa^^^^

Division of a cell

Archaeopteryx

German researchers
show that cells are the
basic unit of both plant
and animal life.

weSl/wng in the same habitats in
different parts of the world often
f look similar because they
have adapted to survive in

the same kind of ecosystem.

1859

The English naturalist
Charles Darwin
publishes the massive
Origin of Species to
support his theory
of evolution. ^

From his careful
experiments, the French
chemist Louis Pasteur
shows that fermentation
is due to micro¬
organisms.

Important fossil discoveries, ~

including that of the dinosaurs, are ^

made during the 1800s. The fossil q
bird Archaeopteryx shows that birds

may have evolved from reptiles.

The finches of the
Galapagos Islands
show distinct beak
variations
brought
^ about by
^ particular
environments.

Modern genetic theory
begins with the rediscovery
of Gregor Mendel’s (1822-84)
forgotten work on heredity in
peas.

Biochemists
demonstrate the
vital importance
for health of minute
L quantities of chemicals like
vitamins and hormones.

—1940s

Health care is improved
dramatically with the ^
mass-production of “
antibiotics. (

\y'%

.% 1953 .

r • The * * *

1 double *

helix #

structure of 4

DNA, the

chemical u

responsible for
heredity, is discovered.
This revolutionizes biology.

The new science of
molecular biology
grows as scientists
explore the nature of
genes and
reproduction.

1990s

Controversial new techniques of
genetic engineering enable
scientists to “design” disease-free
animals, therefore providing a
larger yield of meat.

1980s

Ecologists realise that
the pollution from one
country can cause acid
rain in another
destroying vast areas of
natural vegetation.

Poisonous fumes are
released into the
atmosphere. They mix
with water in the air
and fall as rain.

HOW SCIENTISTS WORK

Men and women leading very different lives and
interested in a range of different topics describe
themselves as scientists. The hospital technician
examining blood samples, the mathematician
thinking about the origins of the Universe, the

botanist collecting rare plant specimens, and the
chemist developing a new type of food flavouring
are all scientists who share a belief in studying
the world to discover how it works and to find
ways to improve our lives.

Surgeons carrying
out plastic surgery

What is a scientist?

Modern scientists are professional men
and women who earn their living by
investigating the Universe around us and
inventing new ways of using its resources.
A few scientists become famous by
making spectacular discoveries, but
millions more make important
contributions to scientific knowledge by
their careful and patient work.

*-4- SCIENTIFIC
EQUIPMENT
Helium-filled balloons like
this carry instruments
into the air to collect
data on temperature,
pressure, and wind speed
at different heights.

This scientist i s calculating the
photosynthetic rate in an oilseed
rape field.

Scientist working on
experiments in genetic
engineering.

COMPUTERS
Scientific experiments often
use computers to work out
lengthy mathematical
calculations quickly and
accurately. They are also able
to store and organize vast
collections of data.

THE REWARDS OF SCIENCE

Scientists value their work because it is
personally satisfying, and because
scientific advances can benefit society.

Nuclear bomb test
in the Nevada
Desert, U.S.A.

POSITIVE AND NEGATIVE
Our modern world depends on
telephones, electricity, cars, and countless
other scientific discoveries and inventions.
Millions of lives have been saved by drugs
such as penicillin and the smallpox
vaccine. But some people hold science
responsible for worldwide disasters
like the atomic bomb, pollution, and
the thinning of the ozone layer.

The research team

Modern scientific experiments are so
complex that people often work in teams,
Each team member contributes his or
her own particular knowledge and
skills. Some scientists organize the
team and their apparatus.

Nuclear plant in Sellafield, England

RESPONSIBILITY
Politicians, economists,
scientists, and other social
planners must jointly decide
whether experiments such
as setting up reactions in a
nuclear reactor, or trying to
correct a baby’s inherited
defects are going to harm or
benefit society.

WORKING ENVIRONMENTS
We usually picture scientists
working in a laboratory, but many
scientific studies need to be
conducted outside. Ecology (the
study of plants and animals in their
habitat), meteorology (the study of
the weather), and horticulture (the
study of crop-growing) are all areas
of science that require experimental
work outside.

Louis Pasteur (1822-95), who discovered a vaccine for rabies.

Alfred Nobel (1833-96)

PERSONAL REWARDS
Many people choose science as a
career because it offers them an
exciting challenge. Making an
outstanding scientific discovery
can bring international fame,
wealth, and important awards like
the Nobel Prize.

HOW SCIENTISTS WORK

Scientific experiments

Experiments are central to the success of science. By trying
out what happens when they slightly alter the natural world,
scientists can collect information that gives them ideas
about how the world works. They can test and compare
different theories to see which one is the most useful for
describing the world’s behaviour, and can develop effective
new equipment, chemicals, and techniques.

OBSERVATION
Some important discoveries -
such as the invention of
electric batteries which
originated in 18th-century
experiments on frogs - are
the result of scientists
observing an unusual event
and appreciating its
significance.

The bending of
light from a
star by the
Sun.

Alessandro Volta with his early battery, 1799.
TESTING

New ideas must be tested to make
sure that they work. Albert
Einstein’s relativity theory was
tested during an eclipse of the
Sun to see if the light from a
distant star was curved - it was.
Pasteur tested his new
rabies vaccine on a boy who had
been bitten by a dog. Scientists
also design experiments to show
which of two competing theories is
better at explaining the world.

COLLECTING INFORMATION

Working like detectives, scientists must carefully
gather together and share detailed information on
everything in the world around them. Scientific
theories are based on interpreting and explaining
this enormous collection of data. Computerized
systems have helped to make the gathering of
information and its analysis more efficient.

Sparks jumped when
lightning flowed along
the kite string to which
Franklin had attached

EXPLORATION

Whether they are investigating the
effects of a new drug, the internal
structure of an atom, the life of a
dolphin, or the nature of the Sun,
scientists use experiments to
explore the nature of the
world.

DEMONSTRATION
Experiments can be useful
for convincing other people
about a scientific theory. In a
dangerous and dramatic
experiment designed to
demonstrate that lightning
discharges are a form of
electricity, Benjamin Franklin
(1706-1790) flew a kite during a
thunderstorm to draw
electricity down from the sky.

SCIENTIFIC TECHNIQUES

All scientific work is carried out
systematically and methodically.
Scientists have developed
various ways of dealing with
different types of information.

CLASSIFICATION
Scientists classify objects to
give nature some kind of order.

Plants and animals are grouped into
families. In the chemical world, the
periodic table puts the elements
into groups to show the
relationships between them.

MEASUREMENT

transmission
electron
microscope
(TEM) is
used
for

studying
micro¬
scopic
cells.

Accurate measurement is crucial for
modern science and engineering.
Scientists must find ways of measuring
enormous distances, such as those
between stars, as carefully as
measuring the size of tiny
biological cells, and the tiny
dimensions of atoms
and molecules.

Satellites are
sophisticated robots that
are sent into space.

EQUIPMENT
Sophisticated apparatus
enables scientists to peer
into tiny atoms, distant
galaxies, and the hidden
secrets of living nature.

MODELS AND THEORIES

Just as globes are used as
miniature models of the Earth,
scientists develop theories,
construct laws of nature, and
build mathematical models to
describe how the Universe works.

THEORIES

Scientists aim to produce theories which
will not only successfully describe the
information they have collected, but which
will also explain how different events are
related to each other, and that can predict
the results of future experiments.

MATHEMATICAL

MODELS
Isaac Newton’s
famous law of
gravity is a
mathematical
model

describing how
the Universe is
held together.

Isaac Newton (1643-1727)

4KS •

J i ff.

» 4f&-m
'w* ‘ j pi s
C

Molecular computer graphic
of DNA model showing the
double helix structure.

PHYSICAL MODELS
,The double helix is a
'physical model of DNA.
It shows the structure of
the chemical that lies at
the heart of heredity.

Safety codes

We all come across dangerous and poisonous codes - a combination of pictures and words -

substances in our everyday lives, but they are not are used as warning symbols. It is essential for
always obvious. To help us identify them, safety your health and safety that you follow these.

Danger
Dust hazard

Harmful

chemicals

Always ask an
adult before using
any substance at
home. Cleaning
fluids in particular
can be extremely
poisonous.

Wear protective
clothes

Wear masks

In the home

Many cleaning materials used
in the home have safety codes
printed on them to show that
they are poisonous if
swallowed, breathed in, or
allowed to stay on the skin.
You should always wash your
hands after using chemicals.
Sometimes
protective clothing
is necessary.

In the school laboratory

Care must be taken when conducting
experiments in the school laboratory.
Some laboratory chemicals are toxic.
Heating others over a Bunsen burner can
be dangerous if the correct procedures
are not carried out. Many substances
have very strong smells, and can cause
unpleasant symptoms if inhaled.

Biological

hazard

Always wear protective
glasses, tie back long
hair and be careful of
loose clothes.

Wear glasses

In the street

Look out for safety codes when you are out
walking in the street. In particular, building
sites and petrol stations can be very
dangerous. Safety codes help
you to avoid accidents.

Radiation

risk

It is against
the law for
pedestrians to
cross some
roads such as
motorways as
traffic speeds
are high.

Wear welding
mask

Wear ear
protectors

Danger

Explosives

Wear boots

pedestrians

* I fcf'sl .

lJU A

JlA

iPy y if

No smoking

Flamma

liquic

4 1

i ,

i i

ass

MATTER

Everything you can think of, from the book that

you are holding, to the chair that you are sitting on, to the
water that you drink, is made up of matter. But matter is
not just things that you can touch. It includes the air
that you breathe. The planets in the Universe,
living things such as insects, and non-living
things such as rocks are also made of matter.

All matter is made of tiny particles called
atoms, which are themselves made up of even
smaller particles, called subatomic particles.
Chemistry involves studying what matter is
made of, and how atoms join together to
make different things.

Creation of matter

Most scientists believe that all the matter in the
Universe was created in an explosion called the
Big Bang (left). Great heat and energy
followed the explosion. Then, after just a
few seconds, some bundles of the
energy turned into tiny particles. The
particles turned into the atoms
that make up the Universe
that we live in today.

FOUNDERS OF CHEMISTRY
The French chemist Antoine Lavoisier
(1743-94) is thought of as the founder of
chemistry. Antoine showed that burned
substances are heavier than unburned
substances. He concluded that this was
because the burned substances gained a
gas, oxygen. Marie Lavoisier (1758-1836)
worked with her husband by translating
scientific works and campaigning for
acceptance of their ideas.

LIVING
MATTER

The Earth is home to
many living things,
including plants and animals of all
kinds. Although a butterfly seems
very different from a rock, they are
both made out of atoms. The
atoms just join up in a different
way to create something else.

Particles of matter

Scientists use a bubble chamber to
identify subatomic particles. The
bubble chamber contains liquid
hydrogen near its boiling
point. Subatomic particles
travelling through the
liquid cause it to
boil, leaving trails
of bubbles.

Although the
particles are
invisible, the
trails that they
leave can
be seen,
and are
different
for each
type of
particle.

Origins of chemistry

Hundreds of years ago, before
anyone knew about atoms, people
called alchemists tried to find out
what things were made of. They
tried to turn metals such as lead
into gold. They also searched for a
medicine that would give eternal
life. They tried without success.
Many alchemists were women. One
name for alchemy, opus mulierum , is
Latin for women’s work.

This page is from a 14th-
century Arab manuscript.

These pictures
show alchemists
at work.

NON-LIVING MATTER
Most matter in the Universe
is non-living. This means
that it does not grow,
reproduce, or move
itself about. A good
example of non-living
matter is the rock that
makes up the Earth that
we live on.

MATTER

THREE STATES

This picture of hot springs, at Waiotapu in New
Zealand, shows the three states of matter, all
together in one place. The rock is a solid, the
water is a liquid, and the rising vapour is a gas.

Gas

A gas quickly fills any space it is put in
because its particles move fast. This
means that a gas has no shape or
volume of its own, but takes the
shape of its container. For
example, this balloon is filled up
with the gas helium. Objects can
pass through a gas easily because j
its particles are far apart. We I*

Liquid

Next time you have a drink, notice
what is happening inside your glass.
The liquid takes on the shape of the
glass. But if you
spill it, the shape

of the liquid changes. If you pour the
liquid into a different container, the
shape of the liquid changes, but the
volume remains the same.

Particles in gases are
far apart and move at
highspeed. They have
little effect on one
another.

Solid

A solid object, such as a book, has a
definite shape that is not easy to
change. This is because the particles
of a solid are linked to one another
by strong bonds into a firm structure.

Particles in liquids attract each
other and stick together in
bundles. These slide past
each other and move about.

Particles in
solids are
tightly packed
together.
They attract
one another
so strongly
that they
cannot move
about: they
only vibrate.

PLASMA

There is a fourth state of matter,
called plasma, but it is not often
seen. It only exists at very high
temperatures inside the Sun and
other stars, or on Earth at low
pressures. It consists of atoms split
up by great heat or electricity. This
ball contains a central electrode
surrounded by gases at low pressure.
Electricity discharges through the gas
in long streaks of plasma, as the
gas atoms are ripped apart by a
high voltage on the electrode.

The particles that result
from the split atoms are
called ions and electrons.

States of matter

MATTER

Using states of matter

Solids, liquids, and gases are all
around you and are used in many
ways. If you have a bicycle, you can see
the three states of matter working
together in harmony. Many parts of
the bicycle are made of solids. Even
the rubber of the tyres is a solid,
although it is flexible, and will
change shape if you go over a bump.
The tyres are filled with air. And the
oil on your bicycle chain is a liquid.

SOLIDS IN USE

A bicycle frame is solid, as are the rim and the spokes
of the wheels. The frame has to be solid to keep the
bicycle together. And the steel rim and spokes on
the wheels ensure that they keep their round
shape, which is important if you want
to cyclfc properly.

LIQUIDS IN USE
All liquids can flow, and some can flow more easily than
others. A liquid’s viscosity is a measure of how fast or slowly
it flows. Water flows easily because it has low viscosity. Oils
flow more slowly, and have higher viscosity . A viscous
liquid such as an oil is used between metal parts
to stop them rubbing against each other. This
is called lubrication.

Pondskaters are so light that the
surface tension of water holds their
weight. Their feet just cause little dents
on the surface.

You can
reduce the
volume of a gas by
squeezing it into a smaller
space. Or you can squeeze more and
more gas into the same space. This is
what happens when you pump up a
bicycle tyre.

Oil on a bicycle chain
keeps all the parts
moving easily and
prevents them from
wearing down.

The piston
transmits the
pressure from
the brake pedal.

Brake pads are
forced against
the wheel by

liquid pressure.

Pressure is
applied to the
brake pedal.

<s?

Pressure travels
through the brake
fluid.

SURFACE TENSION

Particles in water attract each other- they pull
towards each other equally in all directions. But
particles on the surface can only be pulled into the
water by particles underneath - there are no particles
to pull in the opposite direction. This tension creates
a stretchy skin around water that is strong enough to
support the weight of tiny insects.

HYDRAULIC BRAKES
Car foot-brakes work because liquids are
not easily compressed. This means that if
you apply pressure to a liquid, the
force will go right through it. When
a driver presses the brake pedal
down, the pressure goes through
the piston to liquid in the brake
pipes. This makes the brake pads grip *
the wheel disc, which in turn makes.the
wheels stand still. Liquid pressure like this
is known as hydraulic pressure.

GASES IN USE

Unlike solids and liquids, gases do
not have a fixed volume. This
means that you can compress
them, or reduce their volume.
Gases are compressible because
there is plenty of space between
gas particles. When you cycle over
a bump, the air in your tyre is
compressed. So it absorbs the
shock of the bump instead of
passing it through the bicycle.

. Wheel
disc

Find out more

Changes of state p.20
Properties of matter p.22
Bonding p.28
Kinetic theory p.50
Behaviour of gases p.51
Forces in fluids p.128
Sun p.284

MATTER

Changes of state

If YOU TRIED TO STIR hot cooking oil with a plastic
spoon, the plastic would melt. Plastic is soli/i. This means
that it will remain solid at temperatures and pressures
normally found on Earth. But change the circumstances,
and you can change the normal state of a substance. In
the same way, if you put orange juice, normally a liquid,
into a freezer, it will go solid. And if you breathe onto a
cold windowpane, the water vapour in your breath
(normally a gas) will condense into drops of liquid. If the
Sun shines on them, the heat turns them back into a gas
and they evaporate into the air again. Even the hardest
rocks melt at the very high temperatures and pressures
found underneath the Earth’s crust. Most substances that
we know will change state when the temperature or the
pressure changes enough.

From solid to gas

A weight ensures the
pressure remains constant.

A seal round the lid enables
the pressure to build up.

PRESSURE COOKING
The temperature at which a
liquid boils (boiling point) depends
on the pressure around it. When the pressure goes down,
the boiling point goes down, because the molecules can
escape as a gas more easily. When the pressure goes up,
the boiling point goes up, because it is more difficult for
the molecules to escape. In pressure cookers, the increased
pressure raises the water’s boiling point. At the higher
temperature, the food cooks more quickly.

The safety valve allows
excess steam to escape.

If you heat a solid to a special temperature called the melting point, it will
melt into liquid. If you heat it even more, it gets to a point when the liquid
changes into a gas. This is the boiling point. At the boiling point, all
the particles in a liquid get enough energy from the heat to break
free from each other. Then bubbles of gas form in the liquid.

Liquids are always slowly changing to gas, even below boiling
point. This is called evaporation. J0

CONDENSATION

Cold glasses get little droplets of water on
^ them because water vapour from the air
turns back into water on the cold
glass. Cold glass removes
energy from particles
and so turns them
^ into liquid. y CJ

EVAPORATION "
Why does wet ink
dry? Because the
water in it turns into
water vapour
and evaporates
into the air.

Some of the JH

water

particles

get

enough
energy to
escape and
form the gas.

SUBLIMATION
Sometimes a solid turns straight into
a gas. This is called sublimation. It is
what happens with dry ice, used to
make dramatic-looking clouds on
stage in a theatre. Dry ice is really
frozen carbon dioxide. It is called
dry because it does not become
liquid before turning
into a gas.

jr The particles in
j f a liquid move

faster and split up to
Jr become a gas. Or the
* particles in a gas slow
down to become a liquid.

The particles in
a solid move fast
enough to escape as
a gas. Or the particles
in a gas slow down to
become a solid.

The particles in a solid vibrate faster and
particles can move over one another to
create a liquid. Or the bundles of particles
in a liquid slow down to become a solid.

LIQUID

SOLID

ijjfinaMMiaiiBWiMftijjW

MELTING

Particles in a solid are packed
tightly together. But when
heated, they vibrate more and
more until they can break free of
fixed positions, and move freely
over each other. The solid turns
into a liquid. This is what
happens when chocolate melts.

FREEZING

A dripping candle will soon freeze
into a solid if you blow it out. This is
because the particles, speeded up by
the heat of the flame, slow down
again and move closer together when
the heat is removed. When they slow
down enough, they get locked into
position again, f orming a solid.

MATTER

States of water

Water vapour

Water is unusual because it can be

found in all three states of matter in
everyday life. In solid form it is ice, in
liquid form, water, and in gaseous
form, water vapour. The properties of
water in these three states are
important to everything on Earth.

For example, plants and animals
need water regularly to survive.

Evaporation
from land
and rivers

Condei
as rain

ition

snow

Evaporation
from the sea

Most solids are
denser than their
liquid form. But ice
is less dense than
water, and so floats
on the top.

The water under the ice
is warmer than the
outside air, so the seal
and other animals it
feeds on can survive.

WATER VAPOUR
When the temperature is high, water
evaporates quickly. In the warm
tropical forests of South America
there is plenty of rain, and because
the temperature is high, water
evaporates all the time. The water
vapour in the air makes it very humid,
and means that special types of
plants, such as certain orchids,
can thrive. They take all the
moisture they need
straight from the
p air, not from

the ground.

WATER CYCLE

The never-ending cycle between
the different states of water is
essential to everything on Earth.
Liquid water evaporates and solid
snow sublimes into the air. Water
vapour condenses into
droplets to form
clouds. Water
droplets fall
back to Earth
as rain or

snow. ' t i nt- g

The seal gives
out water
vapour as it
breathes.

Pressure on the ice
from the weight of
the skater lowers
the freezing point,
which is why the
ice melts.

STEAM POWER

When water boils, it turns into steam.
'Steam is water vapour that is hot.
Being a gas, it takes up much more
space than the liquid it came from. It
is full of energy and can be used to
drive heat engines such as the steam
turbine. It enters the turbine at high
temperature and pressure, and drives
the turbine wheels round.

Changes with pressure

Pressure can bring about a change of
state. It is possible to ice skate because
skates move over the ice on a thin ^
layer of water. The weight of the
skater is concentrated into the
blade. This causes pressure
under the blade which
makes the ice melt as ^
the skate moves over it. ^PPPBI

Steam goes
into the
turbine under
pressure..

The blades are
forced round, and this ,
movement is used to
generate other types
.of energy, such |
as electricity.

The blade presses
down on the ice.

The ice makes the water
re-freeze behind the skate.

The ice melts
underneath the
blade, allowing it to
glide over the ice.

EXPANDING ICE
Have you noticed how
pipes often burst in
freezing weather? This is
because the water inside
them expands as it
freezes into a solid.

Find.out more

States of matter p.18
Solutions p.60
Chemistry of water p.75
Water industry p.83
Formation of
the earth p.210
Cycles in the biosphere p.372

MATTER

Properties of matter

A SAUCEPAN IS MADE OF STEEL and plastic for a very good reason. The
handle is plastic because plastic is an insulator and it stops the handle
getting too hot and burning your hand. The pan is steel because it is
a conductor and lets the heat go through to the food. Insulation
or conductivity is an example of a particular property of matter.

Some properties, such as conductivity, can be measured. Others,
such as the smell of an object, can only be described.

Scientists measure the properties of many different
materials. They do this at room temperature and
pressure so that they can make accurate
comparisons between them.

You can describe
an orange by its
colour and shape,
how it feels to the
touch, how it smells,
and how it tastes.

NEUTRON STAR

The metal osmium
is the densest
substance on Earth.

It is twice as dense as
lead and over 22 times as
dense as water. But the
densest material in the
Universe is found in neutron
stars. A pinhead of that A pinhead
matter would have a mass of a neutron
of a million tonnes. star #

Water has a relative density of 1
(about 1000 kgm' 3 ). Liquids with a
lower density float on the water
and those with a higher density
sink below it.

A hydrometer is used to __

measure the density of a
liquid. It floats in a container
full of the pure liquid, and
the reading is taken at the
top of the liquid. The
hydrometer floats high
up in a dense liquid,
but lower in a less
dense liquid.

DENSITY

» Different materials
W have a different mass
for the same volume.
The mass (usually in
kilograms, kg) of a
particular volume of a
material (usually a cubic
metre, m 3 ) is its density (usually
given as kg per m 3 or kgm 3 ).
Sometimes, densities are given as
relative densities, a comparison to the
density of liquid water.

The cube of lead is
as heavy as a piece
of wax with a volume
Gases always 13 times greater, and

bubble to the a piece of balsa

surface of a wood with a volume

liquid because 56 times greater,

they have such a
low density. Air
has a relative
density of only
0.0012.

Methylated spirits:
relative density 0.8

Sensing matter

In the everyday world, people do not
usually describe objects in the same
way as scientists do. We rely more on
our senses than on measurements
with instruments. But human senses
are not consistent. They cannot
measure how much something smells,
or exactly what it tastes like, and one
person may sense things in quite a
different way from another.

WEIGHT, MASS, AND VOLUME

You can measure the amount of something

in two ways: by its volume or by its mass.

You buy petrol by its volume (in litres or
gallons) - that is the amount of space it
occupies. Butyou buy potatoes by mass (in
kilograms or pounds) - that is a measure
of the amount of matter in the bag of
potatoes. The volume of something can be
changed by compressing or heating it, but
the mass stays constant.
When gravity pulls on
an object, it creates
a force called weight
which depends on the
mass of the object.

Corn oil: relative
density 0.9

Water: relative
density 1

Lead:

density 11.3
(11,340 kgm- 3 )

Wax:

density 0.9
(900 kgm- 3 )

A tower holds the
cables in place.

Mercury:

relative

density

13.6

Balsa wood:
density 0.2 (198 kgm- 3 )

STRENGTH

Most metals are strong when they are pulled,
so they can be used to build structures such
as this cable-stayed bridge. The road is held
by cables made of steel, which do
not break when they are pulled
by the downwards force of
the road. The pillars that
hold up the bridge are
made of concrete
because it is strong
enough not to break up
when it is squashed by
the force of the bridge
pushing it down.

MATTER

PIASTICITY

If you press some materials, such as dough
or putty, they change shape and stay that
way. These materials are called plastic
materials. There are different kinds of
plasticity, called malleability and ductility.
If a metal can be beaten into thin sheets
without breaking, it is malleable. If it
can be drawn into a fine wire,
it is ductile.

Copper
wire

The plastic
completely
covers the
copper
wires.

MELTING AND
BOILING POINTS
Every pure substance has a
constant melting point and
boiling point at normal air
pressure. But if the substance
is not pure, the melting and
boiling points change. Salt on
snow lowers the melting point,
so it melts to water, and the
weather has to be much colder
before it freezes again.

This silversmith is
making a bowl by
beating out the
silver into the right
shape. This means
that silver is
malleable.

CONDUCTING HEAT
Metals conduct (pass on) heat
well. They have high thermal
(heat) conductivity because of
their atomic structure. Materials
such as plastics and wood have poor
thermal conductivity, so they are
good insulators. This makes them
very useful for covering thermal
conductors. This is why the
handles of kitchen utensils and
saucepans are usually plastic.

Water is a
good thermal
conductor. It
transmits heat
to the metal
spoon.

which is why plastic is
used to cover
conductors such as the
^ wire in a cable.

CONDUCTING ELECTRICITY
Electricity can flow easily through metals, meaning
that metals can conduct electricity. This is because
metals have free-flowing electrons on their atoms.

Plastics, glass, wood, and most other solid materials,
except for carbon, are very poor conductors. They
are electrical insulators,

Copper and some
other metals can be
drawn into wire finer
than a human hair.
This means that
copper is ductile.

If you press wax onto the end
of a metal spoon and onto the
end of a plastic spoon in hot
water, the wax on the end of
the metal spoon will start
to melt first.

EIASTICITY

Rubber has an interesting property. When you pull it,
it stretches. When you let go, it shrinks back to its
original size. This property is called elasticity.
Most materials, even metals, are elastic.
Some materials have an elastic limit,
which means that they do not
return to the original shape
and size if they are
stretched too far.

The balloon
has returned to
its original shape
after being
stretched.

A rubber
balloon stretched
out as far as
possible

Chalk is not very soluble
even in hot water. But
sugar is much more
soluble in hot water. The
hotter the water, the more
soluble sugar becomes.

Chalk in hot water

The boiling point:

liquid turns into
vapour, or vapour
condenses into
liquid. It is always
higher than the
melting point.

BRITTLENESS
Rubber is elastic at normal
temperatures. But this balloon
was dipped in liquid nitrogen,
which has a temperature of-196°C (-385°F). The
balloon became brittle and shattered into pieces when
tapped with a hammer. Some substances, such as glass,
are brittle at normal temperatures. Other substances,
such as clay, are normally plastic, but are brittle after
being baked in a kiln.

Solubility

Many solids, liquids, and gases dissolve
in water and other liquids to form a
solution: they are soluble. Sugar dissolves
in tea, and salt dissolves in water. The
dissolving substances are called solutes,
and the liquids that they dissolve in are
called solvents. Water is often called
the universal solvent because so many
things dissolve in it. This property is
vital to life. Water carries dissolved
substances around in blood and sap. Animals that live
in water get their oxygen as the gas dissolved in water.

Some substances are more
soluble than others. Chalk
hardly dissolves in cold
water. But sugar dissolves
easily, even in cold water.

Chalk in cold water

Sugar in cold water

Sugar in
hot water

The melting (or freezing)
point: solid melts into liquid,
or liquid freezes into solid.

- Find out more -

Atomic Structure p. 24
Transition metals p.36
Carbon p.40
Solutions p.60
Chemical analysis p.62
Floating and sinking p.129
Current electricity p. 148
Factfinder p.402

MATTER

Atomic structure

MOLECULE PICTURE

EVERY SINGLE THING you can see, hear, feel, smell, and taste is made from
microscopic particles. These particles are called atoms, and it would take
millions of them just to cover a full-stop. An atom is itself made up of even
smaller particles. In the centre of each atom there is a nucleus made up of
protons and neutrons. Particles called electrons whiz around this nucleus in
different shells (layers). Protons and neutrons are much heavier than the
electrons, so the nucleus makes up most of an atom’s mass. Some substances,
such as water, are made up of molecules. These consist of several kinds of
atoms joined together in a group. Other substances, such as iron, have just one
kind of atom.

Protons, neutrons, and electrons

This photograph shows 28 carbon
monoxide molecules. They have
been cleverly arranged into the
shape of a person. More than 20,000
of these “people” would be needed
to cross the width of a human hair.

Six protons

Six electrons

The nucleus of every atom contains two types of particle -
protons and neutrons. The number of protons gives the
atomic number. Protons have a positive electric charge,
while neutrons have none. The electrons that spin around
the nucleus, like planets orbiting the Sun, have a negative
charge. But electrons are not solid balls, they are bundles
of energy that move almost as fast as light. There are
always the same number of electrons and
protons in an atom.

CARBONATOM
This drawing shows a carbon
atom sliced in half. The
nucleus of a carbon atom is
made up of six protons
and six neutrons. The
atom’s six electrons
are contained within
two shells.

Carbon-14 has
six protons and
eight neutrons.

ggg

cee

GGQ

Protons, neutrons,
and electrons are
called subatomic
particles.

eee

IGGGQ
! #•••

The commonest
isotope of carbon,
carbon-12, has
six protons and
six neutrons in
its nucleus.

ISOTOPES
All the atoms of an element have
the same number of protons, but some
have different numbers of neutrons. All of these are called
isotopes. An isotope of carbon, called carbon-12, has six
protons and six neutrons in its nucleus. The nucleus of
another isotope, carbon-14, has an extra two neutrons. It is
radioactive. Radioactive isotopes are called radioisotopes.

Carbon atom
sliced in half

The number of shells
an atom has depends
on the number of
electrons it contains.

A bromine atom has 35
electrons in four shells.
Some atoms have as
many as seven shells.

The first shell of a carbon
atom contains two
electrons. The other
four electrons are in the
second shell.

JOHN DALTON

A Greek philosopher, Democritus
(c.460-361 B.c.), put forward the
idea that the Universe was made of
tiny, indivisible particles he called
atoms. His concept was discussed for
hundreds of years. Then, in 1808, the
English chemist John Dalton (1766-
1844) suggested from his experimental
work that each chemical element is made
up of identical atoms, and that elements are
different because they are each made of different
atoms. This became known as Dalton’s atomic theory.

Even in atoms with
many particles,
most of the atom
is empty space.

HOW BIG IS AN ATOM?
Atoms are far tinier than
anyone can imagine. It
would take as many
as 10 million of
them side by side
to measure one
millimetre. Even
though they are
so small, atoms
are mostly made
of space, because the electrons are so far from
the nucleus. If the nucleus were the size of a
tennis ball, the whole atom would be as big as
the Empire State Building in New York.

MATTER

INVENTORS
John Cockcroft
(1897-1967) and Ernest
Walton (born 1903) were
the first to develop a
particle accelerator, in
1932. For this they won
the Nobel Prize for
Physics in 1951. In the
picture, Ernest Walton is
seated inside the counting
room, where the particles are
detected. The long tube above
it is the accelerating tube, and
the hat-shaped part above that
is where the particles start off.

ERNEST
RUTHERFORD

The New
Zealand-born
physicist Ernest
Rutherford
(1871-1937)
discovered in
1911 that atoms
have a tiny, dense
nucleus. Rutherford
and his colleagues were shooting
positively charged alpha particles at
a very thin sheet of gold foil. Alpha
particles consist of two protons and
two neutrons and so have a positive
charge. Most of the alpha particles
went straight through, but some
changed path and some even
bounced back. This showed that
the atom’s positive charge is
concentrated in a small nucleus,
which was changing the paths of
the alpha particles. Most of the
atom is made up of empty space.

Subatomic particles

The protons, neutrons, and electrons that
make up an atom are just three of more
than 200 subatomic particles that are now
known. Scientists are discovering new
particles all the time. They use powerful
machines called particle accelerators to
smash atoms or subatomic particles
together, at high speed, to make other
subatomic particles. They give the
particles weird and wonderful names such
as kaon, upsilon, and charmed lambda.

PARTICLE ACCELERATOR
In accelerators such as a synchrotron (right),
beams of subatomic particles are sent round in
circles by powerful electromagnets, and speeded up
by pulses of electricity. When the particles are
travelling fast enough, they are extracted and made to
smash into each other. Scientists can then analyse the
particles produced.

INSIDE A NUCLEUS

We know that the nucleus of every atom contains protons
and neutrons. And these in turn are made up of smaller
particles, called quarks. The quarks are held together by
other particles, aptly called gluons.

A neutron is made

PARTICLE TRACKS

Scientists often use electronic detectors to
pick up the tracks of particles created by
collisions in particle accelerators. A
computer processes the information and
displays the tracks on a screen. From the
tracks, scientists can work out the mass and
electric charge of the particles that made
them. For example, the green spiral is the
track of a low-energy electron.

Nucleus

Quark

Gluons

SUBATOMIC PARTLQLES

1897 JJ.Thomson (1856T940)
discdyers the electron/

1909' RQbert Millikan (\ 868*,
T953) Wsa surVs the fiegatiVe'
charge op\the Electron. //

1911 Ernfc^t Rutherford ( \6iy-
1937j discovers \hai atbmsXave
a nuclfensA \ \ < / • /// ^

\ \\\ \\ikj /

1913 Niels BUirj/C 1^-1962)
discovers eleat:ropyshells.

1932 James ^ajsMck (1891-
1974) discoverable neutron.

1963 Murray Gefll-Mann
(born 1929) suggests the
existence of quarks.

Particle tracks in a bubble chamber

Find out more

Radioactivity p.26
Bonding p.28
Elements p.31
Carbon p.40
Nuclear energy p. 136
Light p.190
Factfinder p.402

MATTER

Radioactivity

radiation glow

Radioactive materials are often
stored in water. The water acts

Alpha rays are
a stream of
positively
charged
particles, each
consisting of two
protons and two neutrons.

Beta rays are -

a stream of
electrons.

Proton

Neutron

The RADIATION THAT IS USED in hospitals to
treat disease is caused by atomic nuclei (plural of
nucleus) breaking up. Most atoms have stable
nuclei - meaning that the number of neutrons and
protons stays the same. But some nuclei are
unstable and can split up: they are radioactive.
These unstable nuclei have a different number of
neutrons from stable nuclei, and are called
radioisotopes. When they break up, the nuclei give
out radiation. This process is known as radioactive
decay. The larger the number of subatomic
particles in an atom, the more likely it is to be
radioactive. Uranium, for example, has 238
subatomic particles and is
highly radioactive.

Alpha rays
travel at 10
per cent of the
speed of light.

Fuel rods from a
nuclear reactor

Water showing
Cherenkov radiation

as a shield to absorb the
radiation. As the particles travel
through the water, they make it
emit a bluish light. This is
called Cherenkov radiation,
after the Soviet physicist Pavel
Cherenkov, who won a Nobel
Prize for its discovery.

Alpha

radiation

Two stages of
beta radiation

Five

stages of

alpha

radiation

Lead-214

' <£P

Beta radiation

Polonium-214

<8P

Alpha

radiation

Alpha radiation

Three stages of
beta radiation

Polonium■

<£p Lead-206

O *Q

ium-210

RADIOACTIVE DECAY
Uranium-238 is the
most common isotope of
uranium. It has 238 particles
in its nucleus. The number
of nuclear particles goes
down as radiation is given
off in a series of steps. At
each step, a new element is
formed. The rate of this
radioactive decay is called
the half-life; the time it takes
for half the atoms in a
radioactive substance to
decay. The half-life of
uranium-238 is 4,500 million
years, because it takes 4,500
million years f or half the
atoms in any amount
of uranium-238 to
decay radioactively.

MARIE CURIE

The French physicist Antoine
Becquerel discovered the
radioactivity of uranium when
uranium salts unexpectedly
clouded a photographic plate.

Marie Curie and her husband
Pierre Curie then investigated
uranium. They found that its ore,
pitchblende, was so radioactive that
another radioactive element must be
present. They found two, radium and polon
and Becquerel and the Curies shared the 1903
Nobel Prize for Physics for isolating radium.
Marie Curie died of leukaemia, probably caused
by exposure to so much radiation.

Penetrating power

Three types of radiation are
given out by radioisotopes:
alpha, beta, and gamma. They
are all dangerous to living
things. They can pass into living
tissue and damage it. If you are
exposed to too much radiation,
it can kill you. Alpha radiation
is the least harmful. Its particles
cannot even pass through a
sheet of paper. Metal is needed
to stop the beta particles. But
only thick lead or concrete can
stop the powerful gamma rays.

Thick sheet
of paper

1.5-cm sheet
of lead

Uranium loses particles from its
nucleus as it decays radioactively.
Only a few steps are shown here.

1-mm sheet
of aluminium

Uranium-238

Beta rays
travel at 50
per cent of the
speed of light.

Gamma rays
travel at the
speed of light.

RADIOACTIVITY

1896 Antoine Becquerel (1852-
1908) discovers radioactivity.

1898 Marie Curie (1867-
1934)and Pierre Curie (1859-
1906) discover radium and
polonium.

1934 Pavel Cherenkov (born
1904) discovers Cherenkov
radiation.

1934 Irene Joliot-Curie
(1897-1956), Marie and
Pierre’s daughter, and her
husband, Frederic (1900-1958),
show that radioactivity can be
produced artificially.

MATTER

Indicator light

This sensing chamber
contains a radioactive
substance that is used to
detect the presence
of smoke.

GEIGER COUNTER
A Geiger counter detects and measures
the intensity of radiation. It is named
after Hans Geiger (1882-1945), the
German physicist who perfected it. The
detecting probe is filled with gas at low
pressure. The radioactivity splits the gas
into ions, which produce a pulse of
electricity. The needle on the dial or
the speed of the clicks produced
indicate the amount of radioactivity.

Useful radiation

The radiation from radioactive materials can
be deadly, so it always needs to be treated
with care. But it can be put to good use.
Heart pacemakers contain nuclear batteries,
because they last so much longer than
ordinary batteries. Cancers are detected
and destroyed using radioactivity.

SMOKE AI ARMS

Many smoke alarms have a weak radioactive
source such as americium-241. Its rays split
the atoms inside a chamber into ions, which
makes them pass a slight electric current. If
smoke enters this chamber, it disturbs the ions and
reduces the current. A microchip senses this and
triggers the alarm.

The worker is
shielded from the
radiation by leaded
glass walls.

The hat and coat
prevent radioactivity
from clinging to
clothes and hair ..

Ion

Ions and electrons are
created when radiation splits
atoms in the Geiger counter
tube. These then conduct
electricity between the
cathode and the anode
and set off a counter
or loudspeaker.

Anode (positively
charged wire)

Cathode (negatively
charged cylinder)

Radioactivity

Plastic window

Chernobyl

RADIOACTIVE FALLOUT
Nuclear power stations hold
large quantities of radio¬
active material, which is
usually quite safe. But one
of the world’s worst nuclear
accidents was the explosion
at the Chernobyl nuclear
reactor in the Ukraine in April
1986. Radioactive material thrown
into the air eventually returned to the ground
as fallout, contaminating large areas of Europe.
This map shows the contamination ten days
after the explosion.

HANDLING
RADIOACTIVE SUBSTANCES
Radioactive materials must be handled
with care. In the nuclear industry the
workers handle the materials through
special gloves fitted into a cabinet.

Sometimes people have to work
outside a room with the deadly
materials in it, so they use remote¬
handling instruments that mimic the
action of their own hands. All nuclear
workers wear a special badge called a
dosimeter, which records the
amount of radiation they receive
over a certain period.

CARBON DATING

Animals and plants have a
known proportion of a
radioisotope of carbon, carbon-
14, in their tissues. When they
die they stop taking carbon in,
and the amount of carbon-14
goes down at a known rate (the
half-life). Using the half-life, the
age of ancient organic materials
can be found by measuring the
amount of carbon-14 that is left.
This wooden mummy label is
about 2,500 years old.

RADIOTHERAPY
Hospitals use radiotherapy to treat patients suffering
from cancer. In this machine, gamma rays from a cobalt
radioisotope are being focused on a cancer to kill the cells
and prevent the cancer spreading to other parts of the body.
Gamma rays are also used to sterilize medical equipment.

RADIOISOTOPE LABELLING
When certain radioisotopes are
injected into the body, they collect
in, or label, particular organs. This
allows doctors to examine the
organs more easily. The radiation
that the isotopes give off may reveal
damaged tissue. In this false-colour
image of a human heart, the
damaged tissue is the horseshoe
shape on the right of the picture.

Find out more

p.24

Atomic structure
Bonding p.28
Elements p.31
Hydrogen p.47
Nuclear energy p.136
Electromagnetic
Spectrum p. 192
Fact finder p.402

MATTER

BONDING

Sodium atom

COMMON SALT IS MADE OF sodium and chlorine atoms. These
atoms aren’t just mixed with each other, they are stuck together with a
chemical “glue”, known as a bond. All bonding involves the
movement of electrons in the outermost shells of the atoms. But
atoms use these electrons to bond in different ways. In salt, for
example, atoms give away or take in electrons;
this forms what is called an ionic bond. In a
compound such as water, atoms share their
electrons; this forms what is called a covalent
bond. And in metals, the electrons flow around
all the atoms; this is called a metallic bond.
Different atoms stuck together with different
bonds make up the millions of different
chlorine atom substances found on Earth.

One electron
travels from the
sodium atom to
the chlorine atom.

Ionic bonds

An ionic bond happens when an
atom loses or gains one or more
electrons from its outer shell. Each
atom becomes electrically charged
in the process, and is then called
an ion. Ions are either cations or
anions. The atom that has lost
electrons is called the cation,
and has a positive charge. The
atom that has gained electrons
is called the anion, and has a
negative charge. These opposite
electrical charges attract the ions
to each other very strongly. So
most ionic bonds are very difficult
to break. Ionic compounds are
usually solids, and will only melt at
a very high temperature. When
sodium and chlorine atoms form
an ionic bond together, they
become the ionic compound
sodium chloride
(common salt).

Sodium atom

The sodium atom has lost a negatively
charged electron and thus becomes a
positively charged ion, called a cation.

VALENCY
The number of bonds an atom
can form is called its valency.
Atoms have a valency number
which gives you this information.
For example, a sodium atom has a
valency of one. It has one electron
in its outer shell, and eight in its
second shell. It has to give away a
single electron to leave a stable
octet, so it bonds with one other
atom (as in sodium chloride). A
carbon atom has four electrons in
its outer shell. It can bondwith four
other atoms to form a stable octet. It
has a valency of four. Some atoms have
a variable valency: iron can bond with
two or three other atoms.

Atoms bond because it makes
them more stable, and
they are usually most
stable when their outer
shells have eight
electrons. This is
called a stable octet.

LINUS PAULING

The American
chemist Linus
Pauling was born in
1901. During the
1930s, he developed
important theories of
chemical bonding and
molecular structure. He calculated
energies needed to make bonds
and angles of bonds, and measured
distances between atoms. For this
work he was awarded the 1954
Nobel Prize for Chemistry. He was
also awarded the 1962 Nobel Prize
for Peace for his efforts to stop the
testing of nuclear bombs.

The chlorine
atom gains an
electron and thus
becomes a negatively
charged ion, an anion.

IONIC STRUCTURE

In the ionic compound sodium chloride, all the ions
are arranged in a regular structure called a giant
ionic lattice. The crystals of salt are cubes, because of
the basic structure of the lattice. All ionic compounds
form a lattice, but their ions may be arranged in a
different way. This will give the lattice a different
structure, and the crystal a different shape.

Sodium cation

Chlorine anion

MATTER

Covalent bonds

A lot of atoms do not easily lose or gain
electrons to form ionic bonds. Instead
they share electrons between them. The
electrons are shared in pairs called
electron pairs. This type of bond is called
a covalent bond. The smallest part of a
compound with covalent bonds is called a
molecule. The forces that attract the
molecules to each other are quite weak.
That is why so many covalent compounds

Nitrogen has five electrons i n its outer
shell and bonds with three hydrogen
atoms to make a stable octet.

Single bond

Hydrogen atom

COVALENT MOLECULES
This computer simulation shows the three-
dimensional structure of the carbon compound
butane (bottled gas). Butane is a typical covalent
compound. Because its molecules bond to each
other with weak forces, called Van der Waals’
forces, liquid butane easily becomes a gas.

DOUBLE BONDS
In covalent bonds, sometimes atoms
share two pairs of electrons between
them, instead of one. The oxygen that
exists in the atmosphere consists of two
atoms linked together by a double bond.

Hydrogen

Double bond

Oxygen atoms

Water has a high boiling
point for a covalent
substance because the
molecules are linked
by strong hydrogen
J bonds.

HYDROGEN BONDS

A molecule of water (H 2 0) is
made up of two hydrogen atoms
linked to one oxygen atom by
covalent bonds. As well as sticking
together with Van der Waals’
forces, water molecules are held
together with hydrogen
bonds. These occur
when hydrogen
atoms that are
slightly positively
charged are attracted
to slightly negatively
charged oxygen
atoms. The oxygen

Butane flame from
bottled gas in a
camping stove

f Each carbon atom is
bonded to other atoms.

Hydrogen bond

Metallic bonds

In the atoms that make up a
metal, the electrons in the
outer shell are only loosely
attached. These electrons
float around in a common
pool, or “sea” of electrons.
This is metallic bonding.
The sea of electrons can
flow around easily. This
explains why metals can
conduct electricity so well.
When heat or electricity is
applied to one part of the
metal, the electrons quickly
carry it to all the other parts.

Slightly negative
oxygen atom

Slightly positive
hydrogen atom \

A false-colour image
of a gold lattice. Each
yellow dot represents
a gold atom.

Crystalline

Wfk gold nugget

METALSTRUCTURE
Metal atoms are arranged in
rows that fit neatly together,
^ held by a sea of electrons in
f a giant metallic lattice. The

sea of electrons means
that no atom is bonded
to its neighbours, so
the atoms can move
wSB? around and still form
strong bonds in a new
position. This is why metals
are easily bent and hammered.

Find out more

Atomic structure p. c 24
Crystals p30
Periodic table p.32
Chemical reactions p.52
Describing reactions p.53
Compounds and
MIXTURES P.58
Chemistry of water p.75
Current electricity p. 148

The outer electrons
of metal atoms can
move freely from
one to another.

A metal bulb filament glows
as electricity passes through it.

MATTER

Crystals

If YOU LOOK at sugar under a magnifying glass, you will see tiny,
glassy cubes. These are sugar crystals. Gems such as rubies and
sapphires are also crystals. Most solids, including metals, are
made up of lots of crystals. Sometimes you cannot see them
because they are too small or stuck together, but you can
often see them in rocks. Crystals in rocks often have no
definite shape because they are packed together. But when
they grow freely in rock cavities, they form beautiful,
regular shapes. There are seven main crystal shapes, or
systems. These shapes reflect the arrangement of the
atoms or ions that the crystal is made of, called the crystal
lattice. Scientists investigate this lattice with X-rays.

PEGMATITE

The crystals in this rock, called
pegmatite, are large because the
rock cooled slowly. The crystal
shapes are not regular because
the crystals formed right next to
each other, not in a free space.

Emerald

has

hexagonal

symmetry.

Galena (lead
ore) has cubic
symmetry.

Crystal s\stems

The seven basic systems of
crystals are shown above.
Perfectly shaped crystals are
rare, but whatever the shape
of the crystal, its symmetry
can be measured. This helps
scientists to identify it.

CRYSTAL COLOUR

Some crystals, such as sulphur, are almost
always the same colour. But quartz (silicon
dioxide) comes in different colours. This is
because it gets coloured by impurities. In its
pure form, quartz is transparent and is called
rock crystal. But it can be white (milky quartz), pink
(rose quartz), or yellow (citrine). In this purple variety
(amethyst), the colour comes mainly from iron.

CLEAVAGE

When crystals break, they
tend to cleave (split) along
certain planes. The planes
are related to the basic
crystal lattice. Mica, for
example, cleaves into
thin sheets parallel to
the base of the crystal.

WILLIAM BRAGG

X-ray crystallogram
of a protein

William Henry Bragg (1862-1942)
and his son William Lawrence Bragg
(1890-1971) were the first to study the
structure of crystals using
X-rays. They won the Nobel
Prize for Physics in 1915 for their work.
If a beam of X-rays is passed through
a crystal, it makes a pattern on a
photographic plate. This pattern is
called a crystallogram. It reveals the
crystal’s internal structure, which is
the arrangement of the atoms. Each
crystal has its own crystallogram.

MAKING CRYSTALS
This pattern of different crystals
was made from ammonium iron
sulphate crystals (brown), cobalt
chloride crystals (dark blue), and
copper nitrate crystals (light blue).
Crystals are easy t o grow by
hanging a string in water into
which you have stirred a lot of
sugar or bath crystals.

Find out more

States of matter p.18
Bonding p.28
Sulphur p.45
Salts p.73

Chemistry of water p.75
Rocks and minerals p.221
Fact finder p.402

Idocrase has

tetragonal

symmetry.

Gypsum has

monoclinic

symmetry.

Axinite has
triclinic symmetry.

Quartz has

trigonal

symmetry.

LIQUID
CRYSTALS
The displays
you see on
digital watches
and calculators
consist of

transparent liquid crystal held between two
sheets of glass in a certain pattern. When
electricity is passed through the liquid crystal,
it appears darker in the segments needed to
show the right number, while the other
segments stay transparent. This type of display
is called a liquid crystal display (LCD).

MATTER

Elements

seriously began to investigate chemical
elements and compounds. Today,

22 artificial elements have
been created that do not
exist in nature. All are
radioactive. Some
only exist for a few
millionths of a second.

parts fire, two parts water, and two
parts earth. This illustration, from
a 17th-century German poem on
alchemy, shows four characters
symbolizing earth ( Terra ), water
(Aqua), air (Aer), and fire (Ignis).

BIRTH OF THE ELEMENTS

The simplest element, 1 Wr

hydrogen, was the first to By

form, shortly after the Big Wk

Bang, which created the Wfc.

Universe thousands of
millions of years ago. It was y,
followed by helium. .All the
elements that now make up the
Earth were created in the heart of ^0
giant stars. The elements were

scattered through space
when these stars exploded.

ELEMENTS IN PREHISTORY
Iron was one of the elements familiar to
ancient people from about 1500 B.c. The
Hittites, in what is now central Turkey,
found that they could obtain it by
heating iron ores and extracting the
iron. Their knowledge then spread
across Europe. This iron
reaping hook is ^

over 2,000 ? > ^§|jj|£|

>' ears old ' ^ ^*5

Exploding

star

Iron blade fitted
into handle made
from antler.

In this carbon
atom, the six
electrons spin
around,
constantly j

ready to ij

bond with .

other atoms. I

AGE OF THE ELEMENTS
In 1669 a German man named Hennig imm
Brand was probably the first to extract
an element when he discovered
phosphorus. But it was nearly a century
later before others followed him and
heated substances to extract the elements ^
from their compounds. Others separated
elements by electrolysis, which means passing
electricity through a substance.

A 19th-century
laboratory

ATOMS

All the atoms of an element have
the same numbers of electrons in
their shells and protons in the
nucleus. This gives each element
its unique chemistry.

COMMON ELEMENTS
In the Universe as a whole, hydrogen
and helium are by far the most
common elements. They are the /
main elements in the stars,
making up 98 per cent of their
matter. In the Earth’s crust, ^
there is more

Elements in the
Earth’s crust

Rarer elements

Potassium

Magnesium

Sodium

Calcium

Iron

Aluminium

Silicon

Oxygen

oxygen than any
other element, followed by
silicon. Together they account
for nearly three-quarters of the
crust. Carbon, hydrogen, and
oxygen are the most common
elements in the human body,
because they make up the
compounds in all the body cells.

Find out more

LINEAR ACCELERATOR
Nuclear physicists can create a new
element by bombarding an existing
element with high-speed particles
in a linear accelerator. By adding
to the number of protons in the
nucleus, a new element is made.

Atomic structure p.24
Radioactivity p.26
Periodic table p.32
Compounds and
MIXTURES P.58
Fact finder p.402

LO® .

■flgi

ji.ii lj

BUI

ANCIENT ELEMENTS

During the 4th century b.c.,
ancient Greek philosophers such
as Aristotle believed that all forms
of matter were made up of just
four elements, arranged in
different proportions. These were
fire, air, water, and earth. Bone,
for example, was made up of four

A GOLD BAR is made of atoms of one kind only, gold atoms,
which means that gold is an element. Most things in the Universe
consist of combinations of different elements, called compounds.
Only a few elements can be found in the pure state, such as gold,
copper, and silver. So far 112 elements have been discovered, of
which 90 occur naturally on Earth. About ten of these were known
before the 18th century, but most were discovered in the 18th and
19th centuries. It was then that chemists

MATTER

Calcium

Lithium

Beryllium

\6 9

\9.° y

1 11 ^

i 12 i

Sodium

Magnesium

Periodic table

This COMPLICATED-LOOKING TABLE is really a simple
list of all the elements. They are arranged in rows in order
of increasing atomic number, or number of protons in the
nucleus. During the 1860s chemists noticed that certain
groups of elements behaved in similar ways, and tried to
set the groups out clearly in a table. In 1869 Dimitri
Mendeleyev published the best table, which is still used
today. A chemist can tell a lot about an element just by
looking at its position in the periodic table.

Titanium

Cobalt

Copper

Silicon

1 5 1

1 6 1

1 7 1

1 8 1

1 9 1

1 10 1

Boron

Carbon

Nitrogen

Oxygen

Fluorine

Neon

I 13 1

1 14 1

[ 15 1

I 16 1

1 17 1

r 18 i

Aluminium

Silicon

Phosphorus

Sulphur

Chlorine

Argon

1 19 1

/ 20 '

/ 21 N

1 22 1

1 23 1

f 24 1

1 25 1

1 26 1

f 27 1

1 28 1

r 29 i

1 30 1

1 31 1

[ 32 1

[ 33 1

r 34 1

r 35 i

r 36 i

Potassium

Calcium

Scandium

Titanium

Vanadium

Chromium

Manganese

Iron

Cobalt

Nickel

Copper

Zinc

Gallium

Germanium

Arsenic

Selenium

Bromine

Krypton

1 88 1

1 104 1

1 105 1

1 106 1

1 107 1

r 108 1

[ 109 1

89-103

Unq

Unnil-

UnP

Unh

Uns

Uno

Une

Radium

Unnil-

quadium

pentium

hexium

septium

octium

ennium

Iodine

Lanthanum

_ 138.9

1 58 1

y 59 >

1 60 !

1 61 I

r 62 i

1 63 1

1 64 1

1 65 1

1 66 ]

/ 67 \

1 68 1

r 69 i

y 70 x

Cerium

Praseodymium

Neodymium

Promethium

Samarium

Europium

Gadolinium

Terbium

Dysprosium

Holmium

Erbium

Thulium

Ytterbium

Lutetium

175.0

Actinium

1 90 1

1 91 1

1 92 1

r 93 i

1 94 1

[ 95 1

r 96 i

r 97 1

r 98 i

[ " 1

y ioo \

r 101 1

r 102 ^

r 103 ^

Thorium

Protactinium

Uranium

Neptunium

Plutonium

Americium

Curium

Berkelium

Californium

Einsteinium

Fermium

Mendelevium

Nobelium

Lawrencium

The atomic number is the number
of protons in the nucleus. It goes
up one by one along each period.

__ The symbol is a shorthand
way of writing the element
used in chemical equations.

..... The relative atomic mass
is the average mass of
atoms of an element,
compared to the mass
of carbon-12 (taken as 12).

KEY (

0 Actinides

0 Alkali metals 1

0 Poor metals

Alkaline-earth f
n/ metals

0 Semimetals

C] Transition
y metals

0 Non-metals

Q Lanthanides [

0 Noble gases

DIMITRI MENDELEYEV

A Russian schoolteacher, Dimitri
Mendeleyev (1834-1907), collected all
the information about the known
elements and wrote out a card for
each one. Then he arranged the
cards in the order of their atomic
weights to create the periodic
table. He left gaps for elements he
predicted would be discovered, and
the three found in his lifetime
proved him right.

MATTER

The number of electrons for
each element is the same
as the atomic number.

DOWN
A GROUP
In some groups,
such as Group 1,
the alkali metals,
Group 2, the alkaline-
earth metals, and Group 18,
the noble gases, the group
relationship is very obvious:
the elements are similar in
appearance and reactivity
(ability to bond). In other
groups, such as Group 14,
the chemical properties
remain similar, but the
elements change from a
non-metal at the top to
metals at the bottom.

Garbon (G) is a
non-metal, silicon (Si)
and germanium (Ge) are
both semimetals, and
tin (Sn) and lead (Pb)
are both metals.

Carbon

Down a group, the number
of shells increases by one
with each element. An atom
can have up to seven
shells. The number of
electrons in the outer shell
is always the same as the
other elements in the group.

Sodium, from Group 1,
has 11 electrons, with
one in its outer shell.

11 ^

X 12 \

(X 13 X.

X 15 X

X 16 X

X 17 x

X 18

Sodium

Magnesium

Aluminium

Silicon

Phosphorus

Sulphur

Chlorine

Argon

23.0 y

k 24.3 y

k 27.0 y

k 28.1 y

k 31.0

x 32.1 y

*X 35.5 y

X 40.0

Aluminium, from
Group 13, has 13
electrons, with
three in its outer
shell.

Silicon, from Group
14, has 14 electrons,
with four in its outer
shell.

Phosphorus, from
Group 15, has 15
electrons, with five
in its outer shell.

Magnesium, from
Group 2, has 12
electrons, with two
in its outer shell.

ACROSS A PERIOD
Going across the period, the number
of electrons increases by one with each
element, and the chemical properties of the
elements show a gradual change. In Period
3, the elements change from the metal
sodium (Na), through the semimetal silicon
(Si), to the non-metal Argon (Ar). The
elements change from forming cations to
forming anions.

DECREASING SIZE
The number of shells remains
the same across a period, but as
the number of electrons increases,
the size of the atom decreases.
This is because the extra protons
in the nucleus pull the extra
electrons closer to it.

Sulphur, from
Group 16, has 16
electrons with six
in its outer shell.

Chlorine, from
Group 17, has 17
electrons, with seven
in its outer shell.

Argon, from Group 18,
has 18 electrons, with
eight in its outer shell.

Carbon has two
shells.

Groups and periods

How does the periodic table work? The 109 known elements are
arranged in horizontal rows, called periods. The atomic number
goes up as you move across. The periods start with an alkali metal
on the left and end with a noble gas on the right. The atoms of
the elements on the left, at the beginning of each period, have
only one electron in their outer shell. By the end of the period
the outer shell is filled with eight electrons. The vertical columns,
called groups, each contain elements that have the same number
of electrons in the outer shell. So they have the same

valency and behave in a similar way chemically. Germanium

7 7 7 has four

shells.

Silicon has
three shells.

Group 14: carbon (C), silicon (Si),
germanium (Ge), tin (Sn), lead (Pb)

Period 3: sodium (Na), magnesium
(Mg), aluminium (Al), silicon (Si),
phosphorus (P), sulphur (S),
chlorine (Cl), argon (Ar)

METALS AND NON-METALS
Most of the chemical elements are
metals. The non-metals are in a
triangle on the right of the
periodic table. Between the two jj n ^ as fj

are the semimetals, which have shells.

some properties of metals and
some of non-metals. There are
several big differences between
metals and non-metals. Metals are
solid (the one exception is mercury,
a liquid). They conduct heat and
electricity well, and usually have
high melting and boiling points.

They form positive ions (cations)
when they bond with other
elements. Most non-metals are
gases, with low melting and boiling
points. They are not good
conductors, except for carbon. They
form negative ions (anions) when
they bond with other elements.

Lead has
six shells.

Find out more

Atomic structure p.24
Bonding p.28
Elements p.31
Alkali metals p.34
Semimetals p.39
Noble gases p.48
Reactivity series p.66
Fact finder p.402

MATTER

CAESIUM ATOMIC CLOCK

Clocks keep time by “counting”
some kind of rhythm, such as
the swinging of a pendulum.
Atomic clocks “count” the
natural vibrations of caesium
atoms. Scientists know that
caesium atoms vibrate at
9,192,631,770 times per
second, so fractions of a
second can be measured
very accurately using this
clock. The vibrations are
detected with the help of
an electromagnetic field.

Caesium is heated so that it
gives off atoms.

Atoms travelling
through an
electromagnetic field give
a reading on the clock.

Alkali metals

Sodium reacts so quickly with oxygen in
the air that a cut surface
tarnishes within minutes.
Alkali metals are
stored in oil to
prevent this
reaction.

Potassium

reacts even

faster than

sodium with

oxygen in

the air.

reaction with water

A piece of potassium metal reacts so
vigorously with water that it zooms all
over the surface, creating bubbles of
gas. This gas is hydrogen, which burns
with a pink-blue flame. The potassium
and the water react to form potassium
hydroxide, which makes an alkaline
solution in water. When all the metal
has reacted with the water, the water is
warm because of the heat given out
during the reaction. All the alkali
metals react in a similar way with
water. However, rubidium and
caesium explode as they touch it.

Chlorine is
produced at the
graphite anode.

The SALT THAT YOU EAT on your food
contains sodium, the most common element of
Group 1 of the periodic table. All the members
of this group are called the alkali metals, because
they react with water to form alkaline solutions.
Potassium, another member, is an ingredient in
fertilizers, as potassium sulphate, or potassium
nitrate (also called saltpetre). Doctors use
compounds of lithium to treat manic depression,
a mental illness. Also, lithium is mixed with
aluminium to make a light but strong alloy
(metal mixture) used in aeroplanes. All the alkali
metals are a silvery-white colour. Their reactivity
increases going down the group. All have one
electron in their outer shells.

SOAPMAKING

Sodium hydroxide and potassium
hydroxide are boiled with fat to
make hard soap and liquid soap.
It is thought that soap was first
made by the Ancient Egyptians.

MAKING SODIUM
Sodium can be extracted from
salt (sodium chloride), using a
Down’s cell. The salt is heated to
800°C (1760°F) to make it melt.
Electricity travels through the
molten salt, via two rods called a
cathode and an anode, to make
it separate into sodium and
chlorine. This process is called
electrolysis, and was first carried
out by Humphry Davy
(1778-1829).

SODIUM I AMPS
Street lamps glow a vivid
orange-yellow because
they contain sodium
vapour. The colour
is produced when
electricity passes
through this vapour.

Sodium compounds
give a similar colour when

they are held in a flame.

Molten sodium is
drawn off here.

Group 1: lithium (Li), sodium (Na),
potassium (K), rubidium (Rb), caesium
(Cs), and radioactive francium (Fr)

Sodium chloride
is fed in here.

Chlorine is given off.

Molten sodium
chloride

Sodium is
produced at the
circular steel
cathode.

Alkali metals are
soft enough to
cut with a knife.

Find out more

Bonding p.28
Periodic table p.32
Electrolysis p.67
Alkalis and bases p.70
Chemistry in farming p.91
Alkali industry p.94
Electromagnetism p.156
Fact finder p .402

MATTER

ALKALINE-EARTH METALS

Find out more

Periodic table p.32
Compounds and
mixtures P.58
Alkalis and bases p.70
Photosynthesis p.340
Skeletons p.352
Fact finder p.402

CALCIUM, FOUND IN CHALK, milk, and your bones, is one of the
most familiar elements in Group 2 of the periodic table. All these
elements are called alkaline-earth metals because they react with water
to produce alkaline solutions and their compounds occur widely in
nature. For example, beryllium is found in the semi-precious gem beryl.
Radium is the radioactive element discovered by Marie Curie. A
radioisotope of strontium, strontium-90, is a dangerous part of nuclear
fallout, but it is also used to treat skin cancers. In their pure form,
alkaline-earth metals are silvery-white. They have a similar chemistry to
the alkali metals, but they are less reactive. They all have two electrons
in theinouter shells.

Firework

colours

The vivid colours we see
in fireworks are mainly
uced by alkaline-
metals. Magnesium
metal is used in some
fireworks to produce a
brilliant white light.
Strontium compounds
are used to produce
crimsons, and barium
compounds are used
to produce greens.

BARIUM MEAL

In hospitals, some patients have a
“barium meal”, which contains
barium sulphate, before they have
an X-ray. The barium sulphate
blocks X-rays and makes the
digestive system show up on X-ray
photographs. Doctors can then see
if there is anything wrong.

CHALKY FALLS

In hot springs, like Fammukale Falls in Turkey,
warm water bubbles to the surface and cascades
over the surrounding rocks. If it contains a lot of
dissolved chalk (calcium carbonate), this will
come out of solution as the water evaporates, and
be deposited as chalky “icicles”.

LIGHTWEIGHT ALLOYS
Magnesium is widely used
in alloys for bicycle frames,
which also contain such metals
as aluminium and zinc. This
makes them light but strong.

Chlorophyll is the
substance that
makes plants
green.

Chlorophyll
is found in
chloroplasts,
tiny bodies in
plant cells.

BONE CALCIUM

Calcium is a major ingredient of bone,
where it is present as calcium phosphate.
This makes bones hard, so that they can
give structure and protection to other
parts of the body.

VITAL MAGNESIUM
The green pigment chlorophyll is
essential for plants to be able to make
food. Chlorophyll contains magnesium
compounds, which help capture the
energy in sunlight. This energy is used
in the food-making process called
photosynthesis.

MATTER

PFRinnm tari f

Transition metals

Iron, nickel, silver, and gold are typical metals. They are

shiny, hard, and strong. They have high melting points, and conduct
heat and electricity well. In the periodic table these and most of the
other typical metals form part of a central block of elements called the
transition metals. Each of the elements is very similar to those near it in
the table. As well as being typical metals, the transition elements have
other things in common. Many have variable valencies, many are good
catalysts, they form alloys with other metals, and many of their
compounds are coloured.

There are a lot of transition metals.

Some are very well known, but some are
very rare. The more familiar ones
include iron (Fe), cobalt (Co), nickel (Ni),
copper (Cu), zinc (Zn), silver (Ag),
cadmium (Cd), tungsten (W), platinum
(Pt), gold (Au), and mercury (Hg).

SPARK PLUG
The main body and lower
electrode of a spark plug are made
of iron. The central electrode is
usually made of a copper alloy.

Suspension springs are made
of steel with a high percentage
of carbon in it, hardened and
heat-treated to give increased
strength.

Most engine blocks -—
(containing the cylinders,
where the fuel mixture is
fired) are made of cast
iron, which contains a
high percentage of
carbon and other
impurities. It is cheap
and resists shock well.

The generator, the part of a car ^
which produces electricity,
contains coils of fine copper wire.
Elsewhere, perhaps as much as
100 m (110 yards) of copper wire
connect the car’s electrical
components.

Valve springs, which control
the valves that regulate the
flow of fuel mixture, are
made of steel alloyed with
chromium and vanadium,
so that they can resist
high temperatures and
last for a long time.

Transition metals in cars

A car is a good example of something that is made of
many transition metals. The body shell is made of mild
steel, which is iron with a little carbon. The steel also

contains traces of manganese, to improve
its quality and strength. Sometimes
the steel shell is galvanized (coated
with zinc), to protect the steel
from rusting.

Car paints are often made using
transition metal compounds. White
paint may contain titanium dioxide, and
red and yellow paints may contain
cadmium sulphides.

^ The headlamp reflector is
usually chromium plated.
Chromium provides the final
hard shiny coating over base
layers of nickel and copper.

The light bulb contains
tungsten in the coiled
filament. It retains its strength
when white hot,
and is long-lasting.

The bearings in the gear
box are layered, with an
inner lining of relatively soft
bearing alloy containing
metals such as copper, tin,
and lead, and an outer
shell of steel.

IRON FOR LIFE

Compounds containing iron are
essential to living things. In plants,
iron compounds help to make
chlorophyll, the green compound
that produces food. In mammals
iron is found in red blood cells
in haemoglobin, which carries
oxygen round the body.

Stainless steel, which is ii
alloyed with chromium and
nickel, is used for the trim in
various places and sometimes
for the exhaust system.

ZINC

Zinc is often used in batteries. In the
type of battery you would use in a
torch, the zinc makes up the casing.

In the pill-sized
mercury battery,
the zinc is
inside.

An ordinary battery
with the outside
label stripped off to
show the zinc
casing.

This battery is the
type you would find
inside a
watch. ; ■

MAGNETIC METALS
Iron, cobalt, and nickel
are the only transition
metals that can be made
into strong magnets.
Electromagnets have an iron
core that becomes strongly
magnetic when electricity is passed
through surrounding coils. They
are used to move waste iron in
scrapyards. The electricity is
switched on to pick up the iron,
then switched off to drop it.

British/14 Dec 92

MATTER

SILVER

The precious metal silver has been used to make
jewellery for thousands of years. Today it is used most
in the photographic industry. This is because the
compounds it forms with chlorine, bromine,
and iodine are sensitive to light. They are the active
ingredients on a photographic film. The silver
compounds change chemically when light hits them.

This change is made visible during the developing
process, which turns the light-affected compounds to
pure silver. Tiny grains of silver make up the dark
areas on a photographic negative.

PLATINUM

Like gold and silver, platinum
is a precious metal, used to

make jewellery. It is precious
"7n£ : ^£^B because it is rare and
attractive. It also never
corrodes or wears away. This
Hf is also why it is used to make
electrodes and electronic
circuits - they would not work
properly if their circuit metal tarnished.
Platinum’s main use in industry is as a
catalyst, meaning it speeds up reactions
such as the breakdown of oil products.

This small,

square \

electrode is
made of platinum.

It is long-lasting and ^
efficient because it does
not corrode.

NICKEL ALLOYS

Silver-coloured coins are

made from cupronickel, B^^Hb

an alloy of copper and

nickel. Nickel is also

used, along with two other

transition metals, iron and chromium, to make

stainless steel. Nickel is a shiny metal that does

not corrode or tarnish, and it gives these

properties to its alloys. Another interesting

nickel alloy, with iron, is Invar. This is used in

precision measuring instruments because it

scarcely expands or contracts at all when the

temperature changes.

These /
pellets are
pure nickel.

NATIVE METALS

. Most elements are not found native (in a pure

state) in the Earth’s crust, but a few of the
transition metals are. The most important of
these include copper, silver, gold, and platinum.
W Gold has been the most prized metal of all for
centuries. It is one of the most chemically unreactive
elements there is. These gold bars are almost 100 per
cent pure and will never lose their shine.

Each gold bar is
numbered for
security reasons.

Coloured X-ray
of a titanium hip
joint in place.

Once in place, this titanium hip
joint will not react chemically
with the tissues round it. r

INNER TRANSITION SERIES

Part of the transition metals, the inner
transition series consists of two periods on
the periodic table. The lanthanides are in
Period 6, so called because of their first
element, lanthanum. The actinides are in
Period 7 and are named after their first
element, actinium. Within each of these
groups, the elements behave in a similar
way chemically. The lanthanides are so
similar that chemists had difficulty telling
them apart. And besides having similar
properties, the actinides are all radioactive.

GALILEO’S
HF BATTERIES
The U.S. space
probe Galileo, now in orbit around Jupiter,
has nuclear batteries, called RTGs
(radioisotope thermoelectric generators),,
which are powered by plutonium.

TITANIUM

Titanium is a very strong,
unreactive metal. This makes it
useful for implants in the body,
such as hip joints, and to repair or
replace damaged bones.

SAMARIUM IN MAGNETS
Magnets in a loudspeaker help to transmit
the sound. Samarium, one of the lanthanides,
and cobalt make powerful magnets, and so
smaller loudspeakers can be made using
magnets containing
these metals.

Uranium

Samarium

magnet

REFINED URANIUM
The best-known
actinide, uranium,
is the fuel used in
nuclear reactors. It is
extracted from the
ore pitchblende. The
mining of this ore is
carefully controlled
because it is so valuab

Find out more

Radioactivity p.26
Catalysts p.56
Iron and steel p.84
Alloys p.88

Dyes and pigments p.102
Nuclear energy p.136
Electromagnetism p.156
Photography p.206
Fact finder p.402

MATTER

POOR METALS

PERIODIC TABLE

Aluminium (Al), gallium (Ga), indium
(In), thallium (Tl), tin (Sn), lead (Pb),
bismuth (Bi), and polonium (Po)

Some METALS ARE QUITE SOFT AND WEAK, and melt easily.
Although these are known as the poor metals, they are very useful. Tin
and lead were two of the earliest metals used by people because they are
easily extracted from their ores (minerals). They are especially useful in
alloys. Bronze, a mixture of tin and copper, was the first alloy to be
made, in about 3500 B.c. Pewter and solder are tin-lead alloys. Lead is
one of the densest (heaviest) metals in common use. The Romans made
drains out of lead, and their word for lead was plumbum, which is why we
still call our drainage systems “plumbing”. But lead is a serious health
hazard because it gradually builds up in the body and is poisonous.
Another poor metal, aluminium, is one of the least dense
(lightest) of all metals.

The skin of an aeroplane is made
of sheets of aluminium alloy riveted
together. The aluminium quickly
reacts with oxygen to form a
protective coating of its own, so it
does not need to be painted for
protection as iron does.

The inside of an
aeroplane wing is
mostly empty, with a
few "ribs” that hold
\ the outer aluminium
skin in place. This is
fto keep the aeroplane
as light as possible.

k Heavy as lead

Lead has a high density. For this reason it
B is a good barrier to radiation. This is put to
use in the nuclear industry and hospital
HK X-ray departments, where the

staff wear lead aprons. n r in ffTini

^ These aprons are made by
baking a mixture of fine
lead powder and plastic to
make a flexible sheet. This is
then cut out to the right shape.

Lead shot can cause pollution
in the wild. Birds that swallow
it are gradually poisoned by it.

Aluminium

ALLOYS

Aluminium is a soft

and weak metal. It is the metal used to make
kitchen foil. But when aluminium is alloyed
with metals such as copper, it becomes hard
and as strong as steel. Aluminium alloys are
used to build aeroplanes because of their
combination of lightness and strength.

ELECTRICAL USES
Aluminium is a good conductor
of electricity. It is used for the
transmission lines that carry mains
electricity across the country on pylons.
The lines have a core of steel to give
them strength.

LEAD IN GIASS
The sparkle of crystal is the
result of adding lead oxide
to glass. The lead also
makes crystal softer. This
means that designs that will
glitter can be cut into it.

Tin cans

As the pure metal, tin is most used as a
coating on steel, to make tinplate. The
tin is applied by dipping or electrolysis.
Ordinary tin cans are made of tinplate.
Most drinks cans are made out
of aluminium. - }

Find out more

Atomic structure p.24
Periodic table p.32
Reactivity series p.66
Electrolysis p. 67
Aluminium p.87
Alloys p.88
Fact finder p .402

TIN-LEAD

ALLOYS

Pewter, a ®

tin-lead alloy, is

used to make tankards and

ornaments. Solder is another tin-

lead alloy, used to join metals in

plumbing and electrical circuiting.

Tin has two forms, white and grey. The
white form turns into the powdery grey
form at low temperatures. Tin was one
of the elements known to ancient
i civilizations, who combined it with
** copper to make bronze. Bronze was
used to make jewellery and, later, tools.

MATTER

Semimetals

Most of the chemical elements

have definite properties that identify them
either as a metal or a non-metal. But a few
elements have properties that place them in
between. These are the semimetals, or
semiconductors. For example, arsenic looks
metallic, but it is a poor conductor of heat
and electricity. Like a non-metal, it forms
compounds with many metals. Several
semimetals are used in alloys. Silicon forms
part of steel, and antimony forms part of f|
an alloy used to make ball bearings. But
the most important use of semimetals is in
electronics. They are used to make
microchips and other electronic
components (parts).

PERIODIC TABLE

Boron (B), silicon (Si), germanium (Gef
arsenic (As), antimony (Sb), selenium
(Se), and tellurium (Te)

BORON
AND SILICON
Glass is made from sand, which is
one mineral form of silica or
silicon dioxide. Quartz is another
common silica mineral, often
found as attractive crystals.
Heatproof glass contains another
semimetal, boron. The addition
of the boron prevents the glass
from expanding too much and
cracking when it is heated.
Borosilicate glass saucepans
can be put straight onto a
flame. Glassware in laboratories
is also made of this type of glass.

These solar
cells are cut
from a cylinder
of solid silicon.

silicates

Silicon is the
most plentiful
solid element on

Earth. It is most commonly found in the
form of complex compounds called
silicates in clays and rocks. This crystal is a
feldspar, a potassium aluminium silicate,
one of the commonest minerals on Earth.

SOLAR CELLS
Satellites are often designed
to stay up in space for years.

Ordinary batteries would not
last long, so large panels of solar
batteries are used instead. The solar panels
contain thousands of tiny cells of silicon,
which convert the energy of sunlight into
electricity. The panels are positioned so
that they always face the Sun, and as the
satellite travels round the Earth, the
maximum amount of sunlight can be
used to provide energy.

SEMICONDUCTORS
Substances that conduct
electricity only under certain
circumstances are called
semiconductors, and are very
useful. Silicon and germanium
are the most widely used
b semiconductors. Adding

other elements to a
fj semiconductor is called

doping. There are two
JBf possible types of doped
semiconductor, the
p-type and the n-type.
These are joined to
m O form components such
as diodes, transistors,
and microchips which
are essential to modern
electronic circuits.

Resistor

Thousands of electronic
components are crammed
onto the microchips
that form the circuits _
in electronic
equipment.

Potentiometer

Microchip

Capacitor _

Compact disc

Transistor

Special lenses N
focus the laser.

Atoms in the
gallium arsenide
are made to
produce light.

Some of it escapes
in the form of a
laser beam.

The mirror reflects ^
the laser beam onto
the disc so that the
laser can “read”
the pits.

Capacitor

Find out more

Crystals p.30
Periodic table p.32
Glass p.iio
Material design p.ll l
Current electricity p.148
Electronic

COMPONENTS P .168

Rocks and minerals p.221
Fa ct finder p . 40 2

Microchips

COMPACT DISC PLAYER

Music is recorded as pits on a compact disc, and these
are “read” by a low-powered laser beam. The laser is a
diode laser, made from a semiconductor compound
called gallium arsenide. A diode is a device that has
been doped to allow electricity to flow in one direction
only. Diode lasers also transmit signals in fibreoptic
telephone lines.

MATTER

Carbon

PERIODIC TABLE

Group 14: carbon (C), silicon (Si),
germanium (Ge), tin (Sn), and lead (Pb)

Without carbon, no living thing could survive.

We all have carbon in our bodies, and take it in when
we eat our food every day. The carbon atom can bond
with as many as four other atoms from other elements,
as well as other carbon atoms, so there are hundreds of
thousands of different carbon compounds. Carbon is a
non-metal. In nature it occurs in its pure form as
diamond and graphite. In compounds it occurs in
carbonate rocks such as chalk, fossil fuels such as coal,
and carbon dioxide in the air. When fuels burn, the
carbon in them reacts with the oxygen in
the air to form carbon dioxide. But too
much carbon dioxide in the air traps
heat like the glass of a greenhouse.

This is called the

greenhouse effect.

In diamond, _

each carbon
atom is
attached to
four other
carbon atoms.

CARBON BUCKYBALLS
In 1990 scientists discovered a
third allotrope of carbon, besides
diamond and graphite. Its molecular
structure looks like a football or
the domed roof of the stadium
developed by American
engineer Buckminster Fuller. This
form of carbon was therefore
named buckminsterfullerene,
and one molecule is sometimes
called a “buckyball”.

Carbon fibres

Organic textile fibres are
heated to make silky threads
of pure carbon. These fibres
are combined with other
materials such as plastic to
make very strong and light
composite materials. Carbon-fibre
composites are useful for objects
where lightness and strength are
important, from tennis rackets to
small

the best
is over 90 per
cent carbon.

FIZZY DRINKS
The Fizz in drinks is carbon
dioxide. The gas dissolves in
the liquid under pressure,
and bubbles come out when
the pressure is released.

Diamond is the
hardest mineral
known.

When you draw a line with a
pencil, graphite is left as a mark
because the sheets of carbon
atoms are easily pulled apart.

Different forms
of carbon

At first sight, diamond and
graphite seem to have
nothing in common.
Diamond is hard and
clear and graphite is soft
and grey. But they are both
forms (allotropes) of carbon.
Carbon also makes up a large part of
coal. When coal is heated out of contact
with air, it turns to coke, a smokeless fuel.
The charcoal used in barbeques is carbon
made by partly burning wood or bones.

In graphite, each carbon
atom is attached to only three
other carbon atoms in flat
sheets that are weakly
attracted to each other.

Clean water flows
back into the tank.

Activated charcoal
traps dirt and

Carbon
fibres are
much thinner
than human
hair, but are eigh
times stronger
than steel.

Find out more

Tennis
rackets
made with a carbon-
fibre frame are much
lighter and stronger
than wooden ones.

ACTIVATED CHARCOAL

When specially treated, or activated, charcoal has great
powers of adsorption, meaning it attracts materials to its
surface. It can remove poisonous gases or unpleasant odours
from the air. It forms part of gas masks, spacecraft
ventilation systems, and cooker hoods. 11 is also used to
purify liquids, including the water in Fish tanks. The water in
the tank passes over the charcoal, which removes the dirt.
The cleaned water then goes back into the tank.

ELECTRIC CARBON
Carbon is unusual among non-metals
because it is a good conductor of
electricity. In steelmaking, the
electrodes in the electric arc
furnace are graphite blocks.
Electricity arcs (jumps)
between the electrodes
and the metal scrap.
The heat produced
melts the metal.

Periodic table p.32
Organic chemistry p.41
Iron and steel p.84
Coal products p.96
Material design p.1 11
Cycles in the biosphere p.372
Fact finder p.402

MATTER

Organic chemistry

CARBON IS SO IMPORTANT that there is a whole area
of science that studies it. This is organic chemistry. It is
called “organic” because it used to be the study of living
organisms (living things consist of carbon compounds). But
now it is the study of all compounds that contain carbon, except
f»r “inorganics” such as carbonates and carbon dioxide. Carbon
is different from all the other elements because it has a
unique ability: it can form very stable bonds with itself.
Because of this, there are long chains containing
hundreds of thousands of carbon atoms.

Organic compounds can be divided into

families such as proteins, fats, and sugars.

living

CHEMISTRY
Carbon compounds hold
the key to plant and animal life on
Earth. Life is only possible because
of the extremely complex and varied
chemistry of carbon that goes on in
all living cells.

CARBON CYCLE
Carbon circulates through the air,
animals, plants, and the soil all the
time. This is called the carbon cycle.

Brightly coloured fabrics that
do not fade became
possible with
aniline dyes.

Organic
compounds
in animals turn
into organic
compounds and
carbon dioxide
as they breathe
and decay.

Carbon
dioxide
in air

Organic

ORGANIC CHEMISTRY

1808 The Swedish chemist Jons
Berzelius (1779-1848) uses the
term organic chemistry to refer
to the chemistry of living things.

1828 The German chemist
Friedrich Wohler (1800-82),
succeeds in recreating a natural
carbon compound in his
laboratory. The meaning of
organic chemistry now changes
to refer to the chemistry of most
carbon compounds, not just
the natural ones.

1865 The German chemist
Friedrich Kekule von Stradonitz
(1829-96) thinks up the idea of
a ring structure for benzene
after dreaming about a snake
biting its tail.

Animals

compounds in
plants and fuels
release carbon
dioxide during
'^burning. ^

Organic
compounds
in plants
change into
other organic
compounds
and carbon

Animals get
organic
compounds
from eating
plai

the air.

ISOMERS

Some carbon compounds contain the same atoms, but have
different properties. This is because the atoms are arranged in a
different way. Such compounds are called isomers. Butane and
2-methyl propane are isomers of each other. Bottled gas always
contains some 2-methyl propane as well as butane. They are
both made up of four carbon atoms and ten hydrogen atoms.

The benzene
ring has six
carbon atoms and
six hydrogen atoms. S0

6 AROMATIGS
AND ALIPHATICS
Benzene is an organic liquid
with a powerful aroma. Organic
compounds that contain
the benzene ring structure are
called the aromatics. The aromatic
compound aniline, also called
aminobenzene, is the starting point
for a whole range of vivid dyes,
called the aniline dyes. Organic
compounds that are made up of
chains of carbon atoms, with no
rings, are called aliphatics.

The molecular formula of ethene is
C 2 H 4 . This gives the total number of
? carbon and hydrogen atoms. Its
structural formula is CH 2 =CH 2 , which
shows that two hydrogens are attached
to each carbon. The carbons
are linked by a
double bond.

Molecules
of ethene react
to create a long
chain linked by single
bonds. This makes the plastic polythene, with
the formula (CH 2 ) n . The “n” means that the
unit of one carbon atom and two hydrogen
atoms is repeated any number of times.

Butane

POLYMER PLASTIGS
Molecules of carbon
compounds such as
ethene can combine to
form huge chains that
are typical of plastics. The
single molecule is called a
monomer, and the chain
is called a polymer.
Different plastics are
made using different
monomers.

MATTER

Nitrogen

Group 15: nitrogen (N), phosphorus (P),
arsenic (As), antimony (Sb), and
bismuth (Bi)

of the air around us. This element is nitrogen. It is a colourless gas with no
taste or smell, and it forms part of the proteins in every living cell. A
constant cycle keeps nitrogen in our lives. Plants get nitrogen from the soil.
Animals get nitrogen by eating plants or other animals. When plants and
animals die, they rot and return nitrogen to the soil. Nitrogen is also in the
Earth as minerals such as sodium nitrate. Like oxygen, nitrogen in the air is
made up of molecules with two atoms, which have the symbol N2. Nitrogen
forms several compounds with oxygen. These include the gases that come
out of car exhausts and damage the environment.

Nitrogen explosives

Explosives are unstable substances that release
a huge volume of gases quickly. The gases
expand very rapidly and this produces a
devastating shock wave. Most chemical
explosives contain nitrogen, including
nitroglycerine and trinitrotoluene
(TNT). Nitroglycerine is an oily liquid
that is highly unstable. It is made safer by
being mixed with a sort of clay to make
dynamite. Explosives are used to
make bombs.

Explosives can be used
in a very controlled way
to bring down a building
without damaging
others nearby.

Nitrogen
fertilizers
help crops
to grow

Ethanol is
pumped out
here

Nitrogen is fed
in here

Safety valve

NITROGEN FERTILIZERS
Farmers and gardeners apply
fertilizers containing nitrogen
to their soil, to put back the
nitrogen that plants take out.

In the past, rotted manure,
which is rich in nitrogen, was
used. Today, many people
prefer to use artificial fertilizers
such as nitrates and
ammonium sulphate.

Ethanol
is fed
in here

Ethanol
storage tank

NITROGEN
CYCLE
There is a
continuous
exchange of
nitrogen between
the atmosphere,
animals, and plants.
This is called the
nitrogen cycle.

Nitrogen-fixing

bacteria

Fertilizers

Death and A %

decay Nitrogen

to plant

ath and P roteins

UNREACTIVE NITROGEN
Nitrogen is unreactive, so it is used to
exclude oxygen, which is very reactive,
from a range of containers. Ethanol
(ordinary alcohol) is likely to catch fire
if it comes into contact with oxygen, so
nitrogen is used to exclude it from the
storage tanks. Crisp packets are filled
with nitrogen. This excludes oxygen,
which would react with fat in the

crisps and make them go stale.

Nitrogen in animal proteins

LIQUID NITROGEN
Food is quick-frozen using liquid
nitrogen. Foods such as cheesecakes
are loaded onto a conveyor belt in a
tunnel freezer (left). As they move
along, they are first cooled by
nitrogen gas, then sprayed with
liquid nitrogen, which freezes them.

ANAESTHETIC NITROGEN
Dinitrogen oxide is a sweet-smelling gas used as
an anaesthetic. It is called “laughing gas” because
it makes some patients laugh before and after
they are unconscious. In the 19th century,
demonstrations of the effects of laughing gas were
given in private houses in London, England, just for
fun. Later scientists realized how useful the gas could
be as an anaesthetic.

Find out mure

Bonding p.28
Periodic table p.32
Chemistry of air p.74
Ammonia p.90
Chemistry in farming p.91
Rain p.264

Cycles in the Biosphere p.372
Factfinder p.402

MATTER

Phosphorus

Group 15: nitrogen (N), phosphorus (P),
arsenic (As), antimony (Sb), and
bismuth (Bi)

HAVE YOU EVER WONDERED why cola has a sharp taste? The
sharpness comes from phosphoric acid, a compound of phosphorus. In its
common form, phosphorus is a yellowish, waxy, and slightly see-through
solid. It glows in the dark, an effect called phosphorescence. Yellow
phosphorus is so reactive that it must be kept under water to stop it
reacting with oxygen and catching fire. Phosphorus is important in living
things. Plants extract phosphorus from the soil. Animals get it from
plants. In the Earth, phosphorus occurs mainly in mineral phosphates,
most of which are made into fertilizers.

PHOSPHORUS AND LIGHT
Red phosphorus is made by
heating yellow phosphorus
at high temperatures. It is
then rolled into sheets.

Red phosphorus is used
in marine distress flares to
create a very bright light. It
is also an active ingredient in
matches. A safety match will only
strike on a surface containing red
phosphorus. A strike-anywhere
match has a phosphorus
compound in the tip.

MINING PHOSPHORUS
In the Earth, phosphorus occurs
in apatite (calcium phosphate),
which exists in several forms. The
main deposits are in North Africa.
Phosphate rock is used in huge
quantities in the chemical industry
to make fertilizers. The rock is
treated with sulphuric acid to mak
superphosphate, a fertilizer that is easily

absorbed by plants.

Calcium phosphate is part of
bones and teeth, but in nature it
appears as crystals in a variety
of colours and is called apatite.

PHOSPHORUS FOR LIFE

Bones and teeth are mainly made
of calcium phosphate, which makes them
hard. Phosphate groups form part of DNA
(deoxyribonucleic acid) in the
nucleus of cells, which
control^ each cell. A
phosphate called ATP
(adenosine triphosphate)
provides energy in the
body. When it breaks down
to ADP (adenosine
diphosphate), energy is
released for doing
something energetic or for
body functions such as
making muscle protein.

PHOSPHATES
The washing
powder or liquid used
to wash clothes contains sodium
tripolyphosphate. This softens the
water. Phosphates from sewage,
fertilizers, and detergents pollute
rivers because it makes a lot of
algae grow. These then use up the
oxygen in the water. Organic
phosphates are used as pesticides.

DISCOVERING PHOSPHORUS
A German alchemist named Hennig
Brand (17th century) extracted
phosphorus from 50 buckets of urine.
He boiled the urine down and heated
it with sand. Brand chose the name
phosphorus, which means light-bearer
in Greek, because the element glows
in the dark. Brand kept his method
secret, but the Irish chemist Robert
Boyle (1627-91) rediscovered
phosphorus a few years later.

PHOSPHORUS ALLOTROPES

There are three main forms (allotropes)
of the element phosphorus. Pictured
left are sticks and chunks of yellow
phosphorus. But they are slowly
changing into red
phosphorus because it is
much more stable. You can see
the dark patches on the sticks.
Black phosphorus, the most
stable form, can be made by
heating the yellow under pressure.

Find out more

Periodic Table p.32
Alkaline-earth metals p.35
Nitrogen p.42
Chemistry of the body p.76
Chemistry in farming p.91
Soaps and detergents p.95
Cells f.338
Factfinder p.402

MATTER

Oxygen

There IS MORE OXYGEN on Earth than any other element. It is an
invisible and odourless gas, and without it we would all die. We breathe
it in all the time in air, where it is mixed with other gases. Oxygen is
found in many things. In the oceans, it is dissolved in, and forms
part of, water. In the rocks, it is found in most minerals.

Ordinary oxygen is made up of molecules with two atoms,
which have the symbol O 2 . High in the atmosphere, a
three-atom form called ozone is more common. A
protective layer of ozone shields the Earth from
dangerous radiation from space. Oxygen is very
reactive. Burning, rusting, and respiration are just
some of the chemical reactions that happen when
substances combine with oxygen in the air.

RED ROCKS
The atmosphere has not
always contained oxygen. But we know
when it first arrived because it reacted
with the iron in these rocks and
turned them red. The rocks are about
2,000 million years old.

Rust

Iron and steel left in the air and the wet soon
become covered with an orange-brown deposit
called rust. Rust is iron oxide, the result of
a chemical reaction between iron,
oxygen, and moisture.

CUTTING WITH OXYGEN
Oxygen can be used to cut steel. In a
special type of torch called an oxyacetylene
torch, the gas acetylene is made to burn in
pure oxygen to produce a temperature of
over 3000°C (8600°F). This melts the steel
underneath the flame and leaves a cut.
Oxyacetylene torches are also used to weld
steel. The two edges of the steel melt in the
torch flame, and join up as they cool.

Carl

Scheele

EMERGENCY OXYGEN
Patients with breathing problems
or those who are very ill are given
extra oxygen. Their lungs do not
have to work so hard, and so the
patients recover more quickly.

The reaction
between the fuel
and oxygen
cannot take
place without
heat.

The fuel must
contain a
substance
which
combines with
oxygen from
the air.

BURNING
The fire triangle shows
what is needed to make a fire:
oxygen, and a fuel. If any
one of these things is missing, the fire cannot
start or will quickly go out. That is why
covering a camp fire with sand or stones will
make it go out. The sand or stones exclude
oxygen, and so the fire cannot burn.

DISCOVERING OXYGEN
The English chemistjoseph
Priestley (1733-1804) announced
his discovery of oxygen in 1774,
not knowing that the Swedish
chemist Carl Scheele (1742-86)
had found it first one or two years
earlier. They proved that air is not
one element. But neither quite
realized what he had discovered. It
was the French chemist Antoine
Lavoisier (1743-94) who proved,
in 1775, what oxygen is.

Living earth

The atmosphere contains
about 21 per cent oxygen.
When animals breathe, they
take oxygen from the
atmosphere. Plants put it back
again as they make their food
by photosynthesis. Fish and
many other aquatic creatures
breathe the oxygen that is
dissolved in water.

Joseph

Priestley

Oxygen combines
with carbon in the
fuel to make
carbon
dioxide.

Find out more

Bonding p.28
Periodic table p.32
Oxidation and
reduction P.64
Chemistry of air p.74
Cellular respiration p.346
Cycles in the
biosphere p.372
Factfinder p.402

MATTER

DCDinniP TADI c

Group 16: oxygen (0), sulphur (S),
selenium (Se), tellurium (Te), and
polonium (Po)

Sulphur

Without sulphur, substances such as paint
and detergents could not exist. They are made by
a process that uses sulphuric acid, a major
industrial ingredient made from sulphur. Sulphur
is a bright yellow solid. In the ground, sulphur
minerals include sulphides such as galena (lead
ore) and sulphates such as gypsum. Sulphur is one
of the most reactive of all the elements. It reacts
with oxygen to form sulphur dioxide. This gas is
given off in huge amounts by coal-burning power
stations because coal contains sulphur. This causes
pollution in the air. Sulphur is used to vulcanize
(harden) rubber. This makes rubber hard enough
to be made into tyres.

Yellow

sulphur

crystals.

Rhombic sulphur is made
up of molecules with
eight atoms. These
molecules fit neatly
together.

Sulphur crystals

Fine crystals of sulphur are found among
the rocks in volcanic regions of the world.
These are the rhombic shape. Volcanic
vents (cracks) are a major source of sulphur
in countries such as Sicily, Java, and the

United States. The sulphur comes
from gases in the Earth’s
interior.

Monoclinic sulphur is
made up of eight-
atom molecules
with more space
between them than
the rhombic form.

It is only stable above
about 96°C (20FF).

The steam turns
into very hot
water and melts
the sulphur.

The molten
sulphur collects
before being
mixed with air.

SULPHUR ON IO

Jupiter’s large moon, lo, is one
of the most colourful in the
solar system. Its vivid yellow-
orange colour is caused
by the flow of sulphur
from erupting
volcanoes. These
were spotted
by NASA’s
Voyager
probes.

SULPHUR ALLOTROPES
There are two main forms, or allotropes,
of sulphur. The stable form at normal
temperatures is the rhombic form. In both
formsahe sulphur atoms are
arranged in rings of eight.

SULPHUR

BACTERIA

Some bacteria use sulphur instead of
oxygen for energy, so they can only live
on dissolved sulphur compounds. In
the United States they are being used
to release pure copper, and other
transition metals, from their
compounds with sulphur.

PROTEIN
SULPHUR

Egg yolk contains sulphur, which
moves out to the edge of the yolk
to make a grey band if the egg is
boiled for too long. Sulphur is a
vital part of body-building
proteins. When these break
down, they produce hydrogen
sulphide, a poisonous gas that
smells of rotten eggs.

Compressed air is
forced down the
pipe. It mixes with
the molten sulphur
and makes it
lighter.

Sulphur is
forced out i
mixed with
water and
air.

Super¬

heated

steam

EXTRA TING SULPHUR
Sulphur can be extracted from
underground deposits by the
Frasch process. Three pipes are
forced down into the sulphur
deposit. Superheated steam is
pumped down the outside pipe,
which melts the sulphur.

Compressed air is then sent down
the central pipe. It forces frothy
liquid sulphur up to the surface.

Find out more

Crystals p.30
Periodic table p.32
Chemistry of air p.74
Sulphuric acid p.89
Gas products p.97
Industrial pollution p.1 12
Rain p.264
Factfinder p.402

MATTER

HALOGENS

Group 17: fluorine (F), chlorine (Cl),
bromine (Br), iodine (I), and radioactive
astatine (At)

The STRONG SMELL in swimming pools is caused by chlorine, one of
the best-known elements in Group 17, the halogens. Chlorine also forms
part of sodium chloride (common salt). Fluorides, compounds of fluorine,
help prevent tooth decay, so they are added to toothpaste and tap water.
Organic chlorine and fluorine compounds (CFCs) were once heavily used
as pesticides, in refrigerators, aerosols, and packaging. But they are
harmful to the environment, so alternative chemicals have been found
for these jobs. All the silver halides (halogen compounds)
are light-sensitive, so they are used to make photographic
film and paper. Silver bromide is the most commonly
used. All the halogens are highly reactive. All have
seven electrons in their outer shells.

Chlorinating water

Chlorine can be extracted from
concentrated brine (saltwater)
using electrolysis. It is a strong
bleach and disinfectant,
killing harmful bacteria. For
this reason it is used to treat
water in swimming pools and
at water supply plants.
Chlorine is turned into a
liquid for this purpose.

SLIPPERY PLASTIC
A fluorine compound, PTFE
(polytetrafluoroethene), is used as
the non-stick coating on pans
because it is so slippery. Although
it is a plastic, it is not affected by
heat and is very unreactive. This
makes it ideal for saucepans and
ovenware.

SEAWEED IODINE
Traces of iodine occur in sea
water and in seaweed. It is
also important in the thyroid
gland, which controls energy
levels and growth in young
mammals. People lacking
iodides develop a swollen
thyroid gland, called a goitre,
on their neck.

PTFE (also known as Teflon)
works by actively repelling
other chemicals. Even an
egg cannot stick to a
Teflon frying pan.

Clear evidence about the
harmful effect of CFCs
has led to alternative
propellants being used
in aerosol
sprays.

FLUORESCING FLUORITE
Fluorine occurs naturally in minerals such as
fluorite (fluorspar). Fluorite forms cubic
crystals in a variety of colours due to
impurities. Many fluoresce (glow) in
ultraviolet light.

CHI.ORINE
) Chlorine is a yellow-
green, poisonous gas.
Like all the halogens, it
readily combines with
hydrogen and water.
Together they make
hydrochloric acid, a
TB very strong acid.

BROMINE

Bromine is a dark red liquid that
gives off a choking and poisonous
red-brown vapour. Bromine is
one of only two liquids in the
periodic table. As well as being
used in photography,
bromine compounds are
used as mild sedatives.

IODINE

Iodine is a purple-black solid that
turns to gas very easily, giving off a
purple vapour. Iodine compounds,
known as iodides, are used in dyes
and as industrial catalysts. Iodine
dissolved in water is used as a test
for starch.

An ozone hole now
regularly appears in
winter in the Antarctic
over the South Pole.

THE OZONE HOLE
Compounds called CFCs
(chlorofluorocarbons), once used in aerosol cans,
encourage the breakdown of ozone in the atmosphere. The
ozone layer protects the Earth and living things from dangerous
ultraviolet radiation in the Sun’s rays. The ozone layer is so thin
around the South Pole that it is often said that there is a hole
in it. For this reason, CFCs are hardly used today.

Find out more

Bonding p.28
Periodic table p.32
Oxygen p.44
Alkali industry p.94
Industrial pollution p.1 12
Photography p.206
Cycles in the
biosphere P.372
Fact finder p.402

MATTER

Hydrogen

IMAGINE A WORLD without sunlight or heat. This is what would happen
if there were no hydrogen. You cannot see, taste, or smell hydrogen, yet it
is the most plentiful element in the Universe. It is a gas, with many uses.
Much is made into ammonia, which is used to produce fertilizers and
other chemicals. Hydrogenation (treatment with hydrogen) is used to
harden vegetable oils and fats into margarine in the food industry. It also
increases the amount of petrol produced from crude oil. All acids owe
their acidity to hydrogen ions.

IN THE UNIVERSE

Hydrogen is present not only in the stars but
in the clouds, or nebulae, that exist

HENRY CAVENDISH

The English scientist Henry
Cavendish (1731-1810) found a gas he
called inflammable air. But he did not
identify it as the element hydrogen.

He investigated the properties of the
gas and showed
that water is
formed when it is
burned in air. This
proved that water
is not, as had been
thought, a separate
element. Later, the gas
was called hydrogen.

IN THE SUN

Hydrogen makes the Sun shine.

A huge amount of energy is
given out when the nuclei
of atoms of hydrogen join
up, or fuse together, in
the Sun’s searingly
hot interior. This
process is called
nuclear fusion. It
is also used in
the destructive
hydrogen
bomb.

in the space between them.

BALLOONS AND AIRSHIPS
Hydrogen explosions were the cause of
airship disasters in the 1930s, like that of the
Hindenburg on 6 May 1937. Because it is so
light, hydrogen should be ideal for filling
balloons and airships. The drawback is that it
easily bursts into flame, forming an explosive
mixture with the oxygen in the air.

Electron

Fuel of the future

Experimental cars that run on
hydrogen have already been built.

The fuel source is a hydrogen
compound that is heated to release
the hydrogen. The advantage of these
cars is that they cause no pollution
because hydrogen forms
water when it
burns.

Hydrogen-powered car

SIMPLE STRUCTURE
Hydrogen has the
simplest atom there is,
with one proton, which
forms the nucleus, and
one electron.

ON EARTH
There is a lot of
hydrogen on
Earth because it
forms part of water
(H 2 0). It is the
commonest element, with carbon,
in living things and fossil fuels.

Crab nebula

Find out more

Atomic structure p.24
Periodic table p.32
Oxidation and
reduction P.64
Measuring acidiiy p.72
Ammonia p.90
Energy sources p. 1 34
Nuclear energy p. 1 36
Sun p.284
Factfinder p.402

MATTER

Noble gases

PERIODIC TABLE

Group 18: helium (He), neon (Ne),
argon (Ar), krypton (Kr), xenon (Xe),
and radioactive radon (Rn)

BALLOONS THAT SOAR into the air when you let them go are
filled with helium, one of the six gases that fill Group 18 of the
periodic table. These are the noble gases, and they make up
about one per cent of the air. Neon, used in brightly
coloured neon lights, is another well-known noble gas.

Radon is radioactive and is produced by the decay of
radium. It makes up much of the background
radiation that occurs in areas where there are granite
rocks. Noble gases are also called the rare or inert
gases because chemists have been able to make only
a few compounds from them. They rarely
react with anything because they are
so stable: their outer shells are
totally filled with electrons.

Electron

HELIUM

After hydrogen, helium is the lightest gas. It is
lighter than air. That is why it is used to fill
modern balloons and airships. It is safer than
hydrogen because it does not burn. Only a faint
trace of helium is present in the atmosphere.
But some deposits of natural gas contain quite
large amounts, and these are the main
commercial source of the gas.

Outer shell

Complete shells

A neon atom has eight
electrons in its outer
shell. With these, the
shell is complete. The
atom does not need to
lose or gain electrons
by bonding with other
atoms. All noble gases
have a complete outer shell.
This is why they are so unreactive.

WILLIAM
RAMSAY

In 1894, Lord
Rayleigh (1842-
1919) and
William Ramsay
(1852-1916)
discovered the
noble gas argon.
Helium had already
been found in the Sun, and in
1895 Ramsay found it existed on
Earth. He went on to discover
krypton, neon, and xenon in
1898. He prepared the last three
by the distillation of liquid air.
For this work he was awarded the
1904 Nobel Prize for Chemistry.
In 1910, he discovered radon.

GAS LIGHTS

Argon and xenon are used in electric lamps.

Lamps filled with xenon produce an intense blue-
white light. Lighthouses often use xenon arc-
lamps, in which the,light is produced by an
electric arc, a sort of continuous spark. Argon,
mixed with nitrogen, is used in ordinary electric
light bulbs. The inert mixture makes the white-
hot tungsten filament inside a bulb last longer.

Lens

NEON LIGHTS
The colours of this neon rainbow are produced
by passing electricity through the tubes, which
contain a noble gas and other substances at low
pressure. Each noble gas produces a different
colour, and other substances are added for more
colours. Helium gives a yellow light, neon gives a
brilliant red-orange light, argon gives a blue
light, and krypton gives a violet light.

NUCLEAR BY-PRODUCT
Several radioisotopes of
krypton are produced in the
nuclear fission of uranium,
including krypton-85. This
gas escapes from nuclear
power stations. During the
Cold War, the United States
was able to keep track of
Soviet nuclear activity by
measuring the amount of
krypton-85 in the air.

Novovoronezhskaya nuclear
power plant in Russia

Find out more

Atomic structure p.24
Radioactivity p.26
Periodic table p.32
Chemistry of air p.74
Nuclear energy p. 136
Fact finmer p.402

REACTIONS

A chemical in plants called chlorophyll uses
sunlight to convert carbon dioxide and
water into carbohydrates and oxygen.

Silver objects gradually
become dull and blackened
because hydrogen sulphide
in the air reacts with the
silver to produce a thin layer
of silver sulphide.

When we
wash dishes, the
detergent in the
washing-up liquid
breaks down any dirt
and grease and
helps them dissolve
in the water.

The baked cake no longer resembles its
ingredients of flour, eggs, butter, and
sugar. They have been changed
by a chemical reaction.

Baked cake

Melting ice lollies

Scientific
equipment
*vol#Hj| from the

18th century

Physical change

A melting ice lolly is an
example of a physical change.
The lollipop has not changed
chemically - it may look
different, but it still tastes the
same. Physical changes are
not permanent, they are
reversible. The ice lolly can
be made solid again
by cooling it down
in a freezer compartment.

Chemical

CHANGE

Baking a cake is an
example of a chemical change.

Once cooked, the cake does not taste like its
ingredients any more - it is chemically different.
Most chemical changes are permanent or
irreversible - you cannot turn the baked cake back
into flour, butter, eggs, and sugar. However, there
are a few chemical changes which are reversible.

FRANCIS BACON

Francis Bacon (1561-1626) was a lawyer,
experimenter, and great English political figure. In
1620, he wrote a book called New Method, in which
he said that theories about how matter works were
only useful if they were supported by experiments.

ROBERT BOYLE
The Irish chemist Robert
Boyle (1627-91) was one
of the first modern
chemists. In 1661, he
published a f amous
book, The Sceptical
Chymist, in which he
said that ideas should
always be tested by
experiment to see if they
are really true. While
experimenting with
gases, he discovered a rule
about how they behave,
known as Boyle's law.

MODERN IABORATORY
Many scientific laboratories
contain a range of
equipment that scientists
use to carry out different
experiments. For example,
some scientists might study
the reactions involved in
making acid rain so they
can develop ways to prevent
it. Other scientists may use
chemical reactions to make
new materials or to find
cures for diseases.

REACTIONS

Kinetic theory

HAVE YOU EVER WONDERED why you can smell food cooking?
The reason is that tiny gas molecules from hot food whirl through
the air and some reach your nose. Although it is hard to believe,
the atoms and molecules that make up everything we see are
constantly moving. As the temperature rises, the particles move
faster, and so they take up more space. This is the kinetic theory
of matter. The word “kinetic” means moving. Not all particles can
move in the same way. In solids, the particles are closely packed
together and can only move by vibrating or shaking. In liquids, the
particles are still close, but they can move more freely. In a
gas, the particles are widely spaced and move very fast.

Evenly mixed
bromine and air
particles

Heat causes
particles of solids to
vibrate faster than usual.
This explains why the
Eiffel Tower in Paris
expands by 7.5 cm (3 in)
every summer.

Diffusion

Because the molecules in a gas
are moving so fast, gases will spread out and
take up as much space as possible. The way
in which gas molecules spread out is called
diffusion, and it is the reason why smells
travel so quickly. For example, when bread
is baking in the oven, the smell of cooking
soon diffuses through the whole house.

Mixed water and

|—| fl£—ft permanganate

particles

Water

130 *

120 i

BROMINE
DIFFUSION

When bromine is put into
a gas jar, the gas molecules take up all of the
available space. If a second gas jar is added, the
gas soon diffuses into this as well.

BROWNIAN MOTION

In 1827, the Scottish botanist
Robert Brown was surprised to see
that some pollen grains in water
were haphazardly bouncing about.
The great scientist Albert Einstein
explained this movement eighty
years later by using the kinetic
theory. The pollen grains are
being constantly bombarded by
tiny, unseen water molecules. This
type of movement is now called

Brownian
motion.

Magnified
view of
sweet pea
pollen
grains in
water

DIFFUSION IN WATER
If potassium permanganate
is put in water, its purple
colour soon spreads out.
This is because molecules
of water are bumping and
pushing the permanganate
particles. In the same way,
tea left in a teapot will
eventually flavour and
colour all of the water.

Potassium

permanganate crystals
WATER BAGS

A solution of salt and sugar can
cure children with severe
sickness, but many of these
children live in countries
where clean water is not
available. Special bags holding
dry sugar and salt can help. If
they are put into dirty water,
water molecules, but not dirt,
can diffuse through the tiny
holes in the bag, making a
sterile solution ready to drink.

Expansion

If an object, like this
thermometer, is heated, its
ip c particles start to move faster

• III and take up extra space. It is

• said to expand. This is why
railway lines include small
gaps that the metal can
expand into in hot weather.
Liquids expand about ten
times more than solids.
Gases expand about 100
times more than liquids.

Kinetic theory explains how
a thermometer works. An
increase in temperature
causes the alcohol or
mercury inside to expand
and move up the scale.

LUDWIG BOLTZMANN
In the 1860s,
the Austrian
scientist Ludwig
Boltzmann
(1844-1906)
developed the
kinetic theory
of gases. Sadly,
unhappy about
the strong
Opposition from
'other scientists to
kinetic theory,
he committed suicide.

Water molecules can
diffuse through the holes.

Find out more

States of matter p.18
Behaviour of gases p.51
Rates of reaction p.55
Heat p.140

Transport in pi ants p.341
Fact finder p.404

REACTIONS

Behaviour of gases

Liquid nitrogen at
a temperature
of-19&C

The balloon
deflates
in the cold
liquid.

Boyle’s law explains why bubbles from a diver
get bigger as they rise to the water surface.

UHARI.ES’ LAW

A balloon full of air
shrivels up when it is
put in a container of
liquid nitrogen. The very

low temperature causes the air molecules inside
the balloon to slow down. As a result, there are
fewer collisions with the walls of the balloon and the
balloon shrinks. This relationship between the temperature and
volume of a gas was discovered by the French scientist Jacques
Charles in 1787. His law says that, at constant pressure, the
volume of a gas is proportional to the temperature - if the
temperature is halved, then the volume is halved too.

REFRIGERATOR
Inside the pipes of a
refrigerator, a fluid called a
refrigerant continually flows
around. When it passes through a narrow
opening, it rapidly expands to a gas. To
become a gas, the liquid molecules must
take in heat from their surroundings (the
inside of the refrigerator), which become
cold. The gas then flows to a compressor
which forces it back to a liquid. This process
gives out heat, which is why the back of a
refrigerator feels warm.

Narrow

opening

The balloon
starts to
expand as
the gas
molecules
speed up in
the warmer air.

Compressor

AVOGADRO’S LAW
If a container is filled with chlorine
and another identical one with
oxygen, the two containers will
contain the same number of
molecules. This is true even
though each chlorine molecule
weighs twice as much as each
oxygen molecule. This principle
was discovered in 1811 by the
Italian physicist Amedeo
Avogadro. His ^ ^
law says that
equal volumes of
gases at the same
temperature and
pressure contain
the same number

of molecules.

Chlorine

molecule

Oxygen

molecule

The burst balloon
holds very few air
molecules and so
is lighter than the
full balloon.

Hydrogen Oxygen
gas gas

ro « o w 0 i

°0 °QQ
3 o ° ° O'

O o ° I
to°o 0 o Q Pl

BICYCLE pump
A bicycle pump always feels
warm when it is used. This is
because the air molecules
inside it are forced closer
together and so they collide
faster with the walls of the
pump, which get hotter.

The wall of the pump
becomes warm as faster
molecules bump against it.

HEAVY GASES
It is easy to think that as most
gases are invisible, they weigh
nothing. This is not true.

All gases have some
mass as they are made
of particles. If two
balloons full of air are
balanced and then one
is burst, the mass of the
air in the remaining
balloon pulls it down.

GAY-LUSSAC’S LAW
In 1808, the French chemist
Joseph Louis Gay-Lussac
found that when hydrogen
and oxygen react to make
water, two volumes of
hydrogen always react with
one of oxygen. He went on
to discover that when any
gases react together, the
volumes in which they do so
are in a ratio of simple whole
numbers. This is known as
Gay-Lussac's law.

Water

GAS PARTICLES MOVE around freely and very
fast. This is why they can produce dramatic effects
if their temperature, volume, or pressure are
changed. For example, it may be dangerous to
leave a spray can in a hot place. As they become
hotter, the gas particles inside will move faster and
so push harder against the sides of the can. They
may even cause the can to explode. Heating the
can has increased the pressure of the gas inside.
Similar effects were observed in the 17th and 18th
centuries by scientists. They devised laws that are
still used to predict how a gas will behave.

~T* fer

BOYLE’S IAW
Have you noticed that bubbles of
gas are smaller at the bottom and
get bigger as they rise through a
liquid? This is because there is more
liquid pressing on the bubbles and
making them smaller when they are
at the bottom than when they are
near the surface of the liquid. This is
an example of Boyle’s law in
practice. It was discovered in 1662
by the Irish chemist Robert Boyle.

The law states that, at constant
temperature, the volume of a gas is
inversely proportional to the
pressure - if the pressure increases,
the volume decreases.

— Find out more —

States of matter p.18
Changes of state p.20
Kinetic theory p.50
Chemistry of air p.74
Pressure p. 127
Forces in fluids p.128
Heat p. 141
Factfinder p.404

Q O

©°

REACTIONS

Chemical reactions

What is a chemical reaction? it is simply breaking

substances apart and making new ones from the pieces. Whenever
a reaction takes place, new substances, the products, are made.
These have very different properties from the original starting
materials, the reactants. For these new substances to be made,
atoms and molecules must be rearranged. This requires the
breaking and making of chemical bonds. For a bond to break,
energy is needed, while making a bond releases energy. Both occur
in every chemical reaction. The energy can be in the form of heat,
light, or electricity. Reactions that release heat are said to be

\ exothermic. Those in which heat is taken in
| are called endothermic.

Methane and oxygen react
to make carbon dioxide and
water. This diagram shows
how the bonds between
atoms break and rejoin.

Pressing a
cold pack splits
the inner bag.
Ammonium
nitrate dissolves in
the water, making the
solution very cold.

exothermic reactions

When wood burns, its chemical energy is
released in the form of heat. The reaction
involves bond-breaking and bond-making,
but the amount of heat given off by making
bonds is greater than that absorbed by bonds
breaking. As a result, heat is given off and the
surroundings become hotter. This is an
example of an exothermic reaction.

Water

ENDOTHERMIC REACTIONS
Cold packs are used by athletes to cool
down injuries. The cold pack uses a
reaction to take heat from the athlete’s
body. The heat absorbed by bond¬
breaking is greater than that given out
by bond-making. This is an example
of an endothermic reaction.

ACTIVATION ENERGY

Most reactions need a certain
amount of energy to start. This is
why a match will not light until it is
activated by striking it. A candle
will not burn until a match is held
to it. The amount of energy
needed to get a reaction started is
called the activation energy.

The activation
energy is like
a hill that the
reactants
have to
get over.

A lighted match starts
the reaction between
oxygen in the air and
candle wax. Once
started, the reaction
continues
without
help.

Changing bonds

In every chemical reaction,
bonds are broken so that new
ones can be made. Methane,
the main component of natural
gas, has four hydrogen atoms bonded
to one carbon. When burned, it reacts
with oxygen in the air and all the bonds
between the atoms are broken. New
bonds form to make carbon dioxide
and water. As these new bonds have less
stored energy than the original ones,
the reaction gives out energy as heat.

This electric ray (Hypnos
monoptergiumj uses a
reaction that gives out
energy as electricity.

This is used by the ray
to stun its prey.

Lightning causes a
reaction between
nitrogen and oxygen to
make nitrogen dioxide.
This dissolves in water
and falls to Earth as
nitric acid, a component
of acid rain.

REACTIONS
WITH ELECTRICITY
Some chemical
reactions use electricity,
others produce it. An
electric ray, for example,
can kill small fish with a
200-volt shock, through a
reaction in its cells. Lightning
is an electric spark. The energy
it produces can cause reactions
in the air. It causes nitrogen
dioxide to be made f rom
oxygen and nitrogen, and
ozone from oxygen.

The magnesium
in a sparkler reacts
with oxygen in
the air to form
magnesium oxide.
This reaction gives
out energy as light.

A book cover fades because light is
taken in by the dye molecules and
destroys some of the chemical bonds.

REACTIONS WITH LIGHT
When a chemical reaction gives
out or takes in energy, it may do so
as light. A burning sparkler gives
out an intense white light. Posters
and clothes fade in strong sunlight
because a reaction occurs when
light is taken in. Sunlight also sets
off a reaction in our skin to
form the pigment melanin.
This is how people tan.

Find out more

Bonding p.28
Describing reactions p.53
Rates of reaction p.55
Catalysts p.56
Energy conversion p.138
Factfinder p.404

REACTIONS

Describing reactions

Silver Mercury Lead

Ancient symbols

S L

Dalton’s symbols

Ag Hg Pb

Modern symbols

SYMBOLS AND FORMUIAE

In ancient times, seven elements were known, each of
which was depicted by a different planet. Around 1800,
the English chemist John Dalton devised a set of picture
symbols for the known elements. In 1811, Swedish
chemist Jons Berzelius invented the system we now use
where letters represent elements. These letters can be
put together to show a compound’s chemical formula.

CHEMICAL FORMULAE and chemical equations are the
chemist’s equivalent of shorthand writing. They are used to
describe chemicals and their reactions. The chemical formula
of a compound (combination of elements) shows which atoms
it contains and in what proportions. A chemical equation is
used to describe a chemical reaction. Like a cookery
recipe, an equation gives a list of ingredients
and the proportions in which they need to be
mixed. It also shows what will be produced
during the reaction. Chemical equations
overcome problems of language. They are
used by chemists to tell other scientists all over
the world about what they have
seen during their experiments.

The two clear
solutions are
mixed and a
yellow solid,
lead iodide,
is formed.

Solution of potassium
iodide in water

Calcium Carbon Oxygen

Solution of lead
nitrate in water

FORMUIAE
EVER WHERE
Every compound
has a chemical
name as well
as a formula
showing the
elements it
contains. For
example, the
chemical name
of chalk is calcium
carbonate. Its chemical formula is CaC0 3 .
This tells us that in chalk, for every atom
of calcium (Ca), there will be one atom of
carbon (C) and three atoms of oxygen (O).

This is an example
of a double
decomposition
reaction in which
two compounds
in solution
swap partners.

Word

equation

Symbolic

equation

potassium iodide

2KI(aq)

lead nitrate

/ /

Pb(NO s ) 2 (aq)

lead iodide

potassium nitrate

To make a balanced
equation, the number of Kl
molecules (and the number
of KN0 3 molecules) must
be doubled.

Chemists use symbols that show what
state the chemical is in. (s) means solid,
(!) means liquid, (g) means gas, and
(aq) means dissolved in water.

Pbl 2 (s) + 2KNO s (aq)

--This 2 shows there are two nitrate
groups joined to each lead atom.

LAW OF CONSERVATION OF MASS

MOLES

Because atoms and molecules are so
tiny, chemists count them by mass.

The mole is their counting unit. A
mole of any substance contains
6 x 10 23 particles, but each substance
has a different mass (its molecular or
atomic mass). Using the mole to count
particles is just the same as a banker
counting coins by weighing them.

One mole of lead tetraoxide
contains 6 xIO 23 molecules.

It has a mass of 685 g.

Equations

A reaction can be described in different ways.
One way is to write an equation. This can be in
words or with chemical formulae. If chemical
formulae are used, the equation must balance;
that is, it must have the same numbers of the
same atoms on each side. Only a balanced
equation can show the proportions in which
the chemicals react together.

Ooooo^
QooQooO

One mole of aluminium contains
6 xIO 23 atoms. It has a mass of 27 g.

6 xIO 23 is known as Avogadro’s constant.

VALENCY

The number of chemical
bonds an atom can make is
called its valency. It is the
number of electrons an atom
gains, loses, or shares when it
forms a bond. To form a
compound, the total of the
valencies of each element must
add up to the same number.

When the compound aluminium «r

oxide (Al 2 0^) is made, 2 atoms of
aluminium combine with 3 of oxygen.

Aluminium (A!)
has a valency
of 3.

Oxygen (O)
has a
valency
of 2.

When a chemical reaction occurs,
nothing disappears, the atoms are
just rearranged. An equation must
therefore be balanced. The
number of atoms on each side
must be the same. This is the law
of conservation of mass. It says that
the total mass of the substances
produced in a reaction equals the
total mass of materials used.

Find out more

Bonding p.28
Periodic table p.32
Chemical reactions p.52
Compounds and mixtures p.58
Fact finder p.404

REACTIONS

Reversible reactions

IMAGINE TRYING TO MAKE a log of wood from its
smoke and ashes. Most chemical reactions, like burning,
only go in one direction. Once they have happened, they
cannot be reversed. They are irreversible. But not all
chemical reactions are like this. Sometimes it is possible to
reverse the change that has occurred. For example, when
an alkali such as washing soda is added to red cabbage
juice, the juice turns green. If an acid, such as vinegar, is
then added to this green juice, the juice is turned back to
its red colour. Such reactions are reversible. Reversible
reactions have a forward reaction (red juice to green
juice) and a backward reaction (green juice to red
juice). In fact, both reactions are happening at the
same time, but depending on the conditions, one
may be stronger than the other.

Equilibrium

In a reversible reaction, after a time it
will look as if nothing is happening.
In fact, both the forward and
backward reactions are
continuing, but at the same
speed. This is chemical
equilibrium. In the same way,
if you are using a running
machine, you will stay in the
same position if you run at the
same speed as the machine. If the
machine speeds up, you will move
backwards. To reach equilibrium
again, you need to speed up too.

IRREVERSIBLE CHANGE
When paper burns, carbon dioxide gas,
water, and black carbon soot are
produced. These cannot be turned
back to paper again because burning
paper is an irreversible reaction.

LE CHATELIER’S PRINCIPLE
A change in temperature,
pressure, or concentration
during a reversible reaction
will change the speed of either
the forward or backward
reaction. If cooled, for
example, the reaction that
gives out heat will speed up, so
as to cancel out the effect of
the cooling. Such effects are
summed up in Le Chatelier’s
principle. This says that if a
change is made to a reaction in
equilibrium, the reaction will
adjust itself to cancel out the
effects of that change.

Nitrogen
atom

Oxygen
atom

Nitrogen dioxide

Nitrogen —^

dioxide T“
gas

Scientists
use this sign
to show that
a reaction is
reversible.

Nitrogen
monoxide
and
oxygen
gas

NITROGEN DIOXIDE
If brown nitrogen dioxide gas is
heated, the colour becomes
lighter and lighter until at 620°C
(1148°F), the gas is totally
colourless. This is because it has
broken down into nitrogen
monoxide and oxygen, both of
which are colourless gases. On
cooling, the changes are reversed.

Nitrogen monoxide
and oxygen

The reaction is in
equilibrium. The
forward and
backward reactions
are continuing at the
same speed.

If more of the
products are added,
the backward
reaction will speed up
so as to use up the
extra ingredients.

If more of the
reactants are added,
the forward reaction
will speed up, so that
the extra reactants
are used up.

HENRI LE GHATELIER
Born in Paris, Le Chatelier
(1850-1936) worked for
some years as a mining
engineer before he took
up a teaching post at the
University of Paris. He is
remembered for his theory,
Le Chatelier’s principle.

CHEMICAL CLOCKS
Some reversible reactions do not settle
down to an equilibrium. Once started,
they continue to oscillate backwards
and forwards. Sometimes this
produces amazing colour changes.
One moment a solution may be blue,
and the next moment, red. Because
these oscillations occur at regular
intervals, these reactions have been
called chemical clocks.

These photographs
of two chemical
clock reactions
were taken at one-
minute intervals.
They show how
waves of colour
move through
the reaction.

Find out more

Changes of state p.20
Nitrogen p.42
Oxygen p.44

Chemical reactions p.52
Rates of reaction p.55
Measuring acidity p.72
Ammonia p.90

REACTIONS

Rates of reaction

COAL EXPLOSION

A large piece of coal will not react with air
unless we light it. A mixture of coal dust
and air, however, can react rapidly and
explosively, as in a coal mine explosion.
This is because coal dust has a larger
amount of surface that can react.

Coal dust
particle

Oxygen

molecule

Oxygen molecules
can only reach the
surface coal particles.

In coal dust, there are
many coal particles
available to react with
the oxygen molecules.

EXPLOSIONS OCCUR very quickly. Other reactions occur more
slowly - a bicycle might take several years to rust. In our lives, we
of ten want to alter the rate (speed) of a reaction. When we put milk
into the refrigerator, we are slowing down the rate at which it turns
sour. Chemists also want to control the rate of reactions. Industrial
chemists want to speed up reactions to lower costs. Environmental
scientists want to slow
down reactions that
can damage the Earth.

Many factors can affect
the rate of a reaction.

The important ones are
temperature, pressure,
concentration, light,
and surface area.

Material dipped in a
concentrated solution of dye
colours very quickly. The
rate of reaction is fast.

Material dipped in a weak
solution of dye colours
slowly. The rate of
reaction is slow.

•U

Otze, a 5,000-year-
old male body
found in a glacier
between Italy
and Austria in
1991, was well
preserved. His
body would
normally have
been reduced to
bones, but the
low temperature
slowed down his
decomposition.

EFFECT OF TEMPERATURE
Most reactions go faster at higher temperatures.
This is because the reacting particles have more
energy and move faster. They are more likely to
bump into one another with enough energy to
cause a reaction. In the cold, all chemical
reactions are slowed down. This is why a
refrigerator is used to preserve food.

EFFECT OF LIGHT
Biodegradable plastics
will decompose more
quickly in strong
sunlight than in a
kitchen cupboard.
This is because some
reactions are speeded
up by light. Light
gives the reacting
molecules more
energy to move.

EFFECT OF
SURFACE AREA
The surface area of a
solid is the amount of
surface on the outside.

This can affect the rate
of reaction. Chipped
potatoes are quicker to fry
than whole ones as there are
more exposed particles on
the surface of the potato chips
which can react with the hot oil.

Potato is often cooked in a
deep fat fryer. Big chunks
take a while to cook, but
thinly sliced pieces will
cook in seconds as they
have a larger surface
area for their volume.

EFFECT OF CONCENTRATION
If you wanted to dye some material quickly,
you could make the dye solution very
concentrated. A concentrated solution has a
lot of dye particles dissolved in it, so there are
more particles to collide with the material and
cause a reaction. A weak solution, on the other
hand, contains only a few dye particles and
would cause a slow rate of reaction. For the
same reason, anything will burn very quickly
in air with a high oxygen content.

COLLISION THEORY

For a chemical reaction to happen, the
reacting particles must bang into, or collide,
with each other with enough force or energy
(the activation energy) to break bonds. This
is collision theory. If the particles do not have
this energy, they will just harmlessly bounce
off one another. It is like stock car racing,
where two cars need to bump into each other
with a lot of force in order to cause damage.

If two particles meet,
they may rebound with
no reaction, but if they
collide with enough
force, a chemical
reaction will occur.

EFFECT OF PRESSURE
Particles in a gas are wide apart.

But if the pressure is raised, they
are brought closer together and are
more likely to bump into and react
with one another. In a machine
called an autoclave, high pressure
is used so that objects can be very
quickly sterilized by steam.

Find out more

Kinetic theory p.50
Chemical reactions p.52
Catal\5ts p.56
Solutions p.60
Chemical industry p.82

REACTIONS

Catalysts

Reacting molecule trapped
in the pore of a zeolite

Zeolites

The zeolites are an
amazing family of catalysts.

These occur naturally in
volcanic rocks, but they can be
made artificially as well. They are
usually made up of aluminium,
silicon, and oxygen atoms joined
together in a beautiful honeycomb
structure which contains millions of
holes or pores. During a reaction, the
reacting molecules are trapped in
these pores while they react with each
other. The size of the pores is very important, as only molecules
of a particular size can enter and undergo a chemical reaction.

1 HE MAGICIANS of the chemical world, catalysts.can
alter the speed of a reaction but are left unchanged once
the reaction has finished. They work like an introduction
agency, introducing the reactants to one another.

Around 90 per cent of all chemicals are made using a
catalyst. Artificial catalysts are used in the manufacture of
petrol, plastics, fertilizers, medicines, and synthetic
fibres for clothing. Enzymes are natural catalysts
that control the way our bodies work. Usually, catalysts
are used to speed up a reaction. But they can also be
used to slow down a reaction, a process known as
inhibition. For example, chemicals called antioxidants
are added to food to prevent it rotting too quickly. The
word catalyst was first used by the Swedish chemist Jons
Berzelius, and means “to break down”.

Catalysts lower the
activation energy of
the reaction.

REACTION PATH
To speed up a reaction, catalysts
provide an easier pathway for the
reaction to follow. Imagine a cycle
race in which one team struggles
over the top of the mountain, while
the other team freewheels down a
lower path. The path over the
mountain is like the normal route
for the reaction. The lower path is
the route the catalyst provides.

Zeolites were
named after
the Greek
words for
boiling stone
because when they
are heated, water is driven out
of the millions of channels that
they contain, leaving a very
effective catalyst.

This is a selection of different
catalysts. They come in all shapes
and sizes, but they must always
have a large surface area.

METHANOL

Methanol is a clear liquid that can
be stored in a bottle for a hundred
years without changing. But if it is
passed over a heated zeolite
catalyst, it immediately undergoes
a chemical reaction and is
converted to petrol. This
remarkable reaction is
used in New Zealand as
part of a process
for converting
natural gas

Have you noticed the fizz
that sugar makes when it
is put into a fizzy drink?
The sugar is acting as a
catalyst for the dissolved
carbon dioxide gas to
come out of solution.

These holes control the
size of the molecules
that can enter. By
altering the size
of the holes,
chemists can
create a zeolite
suitable for
a certain
reaction.

Zeolite

structure

SURFACE AREA
Most catalysts work by bringing
the reactants close together.
They do this by forming a
temporary bond with one or
both of the reactants. So it is
important for a catalyst to have
a large surface area, as this is
where the reaction takes place.
For instance, a spoonful of a
zeolite has the same surface
area as two football pitches.

Melhano! Petro |

FUEL CELLS

Even astronauts rely on catalysts. To send
people into space, you need a power
supply for the spacecraft, and a supply
of water for the crew. The fuel cell
provides both of these. It uses a metal
catalyst, usually platinum, to convert
hydrogen and oxygen into water. This
reaction produces electricity. In this
way, a fuel cell can provide all the
energy a spacecraft needs, as well as
all the water needed f or drinking,
washing, and rehydrating dried food.

REACTIONS

WILHELM OSTWALD

Born in Latvia, Wilhelm Ostwald
(1853-1932) spent most of his life
in Germany. He carried out
research into catalysts at a time
when the idea of a chemical that
could drastically alter the speed of
a reaction seemed ridiculous.
Ostwald persevered and showed
the world how
extremely useful
catalysts can be
by developing a
process for
converting
ammonia into
nitric acid. In
1909, he was
awarded the
Nobel Prize for
Chemistry.

are

clear by
enzymes.

Enzymes in washing
powders help to break
down stains.

Enzymes

Nature produces remarkable catalysts called

enzymes, without which the thousands of

reactions in the human body would be
so slow that life could not go on.
Enzymes in our bodies catalyze
the breakdown of our food
and help to make

important chemicals
such as proteins.
Today, enzymes
are even used in
industry to make
washing powder,
medicines, and
fruit juices.

Inside the convertor
is a honeycomb
structure,
coated with a
tiny amount
of the metals
platinum and
rhodium. These
metals are
the catalysts.

Unlike other catalysts, an enzyme will only
catalyze one type of reaction. Just
as only the correct key will fit a
lock, the reacting molecules
must be exactly the right shape
to fit the enzyme molecule.

Exhaust
gases
containing
carbon

monoxide, nitrogen
oxides, hydrocarbons,
and air enter the catalytic
convertor at one end.

Mineral wool
soaked in
paraffin oil

Heat

LABORATORY CRACKING
Broken china can be used as a catalyst
to break down paraffin oil. This is
known as a cracking reaction. If
mineral wool soaked in paraffin oil is
put in a test-tube, and heated so that
the oil passes over the china, the
bonds in the large oil molecules are
broken. Smaller, lighter gas molecules
are made and can be collected.

CATALYTIC CONVERTOR
Some cars contain a catalyst called a catalytic
convertor. This changes the toxic exhaust gases that
would pollute the atmosphere into less harmful gases.

It is made of a thin coating of two metals, platinum and
rhodium, on a solid honeycomb support. Because lead
can poison platinum and rhodium (it will stick to them
and prevent any reactions from taking place), cars
with catalytic convertors must use lead-free petrol.

In the convertor, carbon
monoxide and the
hydrocarbons are
converted into
carbon dioxide and
water. The nitrogen
oxides are converted
to nitrogen. These less
harmful gases are
released into the air.

GATALYHC CRACKING
Molecules with very
long chains of
carbon atoms are
more useful if they
are heated and
broken down into
smaller pieces,
but this process
requires very high
temperatures. By
using a catalyst
such as a zeolite,
this splitting, or “cracking”
process is made much easier
and quicker. In this way,
large crude oil molecules
can be turned into smaller,
more useful ones, such as
those that make up petrol.

The

exhaust gases
form temporary bonds
with the surface of the catalyst.
This brings them into close contact
and allows the reactions to occur.

Bubbles of gas
forming. Small gas
molecules have been
made from large oil
molecules.

QQQ

ENZYME WASHING POWDERS
Biological washing powders
contain enzyme catalysts that
help to break down stains.
Because enzymes are destroyed
at high temperatures, biological
washing powders are not
effective in very hot water.

Ozone layer
over the
Arctic

OZONE CATALYST
Chlorine from the decomposition
of chlorofluorocarbons (CFCs) is
the catalyst for the breakdown of
ozone to oxygen in the upper
atmosphere. As with all catalysts,
the chlorine is left unchanged at
the end of the reaction and so can
go on to more ozone destruction.
This is what is causing a hole in
the ozone layer.

Find out more

Chemical reactions p.52
Rates of reaction p.55
Compounds and

MIXTURES P.58

Chemistry of the body p.76
Oil products p.98
Digestion p.345

REACTIONS

Compounds and mixtures

ELEMENTS THAT EXIST on their own are rarely found in the natural
world. Most substances are made up of two or more elements that bond
in different ways to form compounds. In a compound, atoms of different
elements bond in a chemical reaction. Once this reaction has taken place,
it is very difficult to separate the different elements of the compound.

Water is a good example of a compound. It is made up of two atoms of
hydrogen combined with one of oxygen. Combining elements to form
a compound is very different from just mixing them together. Mixtures
are combinations of different elements or compounds. Sea water, for
example, is a mixture of water with other compounds, such as salt. But
unlike compounds, no chemical reaction takes place when the elements
or compounds mix together. This means that it is usually possible to
separate mixtures into their different parts.

IRON AND SULPHUR

A mixture of iron and sulphur contains separate iron and
sulphur atoms. If this mixture is heated, a chemical reaction
occurs and a new compound, iron sulphide, is made. Iron
sulphide contains iron and sulphur atoms joined together
and has very different properties from the mixture.

Heat source

BUILDING BLOCKS
just as letters of the alphabet can
be used in different combinations
to make millions of words, the
elements can be arranged to make
countless different compounds.

The elements are nature’s building
blocks. Like a handful of building
bricks, they can be used to build
many different chemical structures.

When iron filings are mixed with
sulphur in a watch glass, you can
still see the black iron specks in
the yellow sulphur powder.

The iron from the iron and
sulphur mixture can be pulled
away by a magnet. As the
iron is in a mixture, it has
kept its magnetic properties.

The iron from the iron
sulphide cannot be pulled
away by a magnet. As the
iron is in a compound,
it has not kept its
Q magnetic properties.
- ©

Iron sulphide
molecule

Iron sulphide is a black shiny
compound with different properties
from those of its elements.

In a mixture,
iron filings can
be separated
from sulphur
using a magnet.

Properties of

COMPOUNDS AND MIXTURES

A compound, such as iron sulphide,
is very different from its elements,
but a mixture keeps the
properties of the
substances it contains. It is
Magnet difficult to separate a compound into its elements, but a

mixture can be separated quite easily. A mixture of iron and sulphur,
for example, can be separated by removing the iron with a magnet. A
compound always contains the same proportions of its elements. Iron
sulphide (FeS) always contains one part of iron to one part of sulphur.

The amounts of the different substances in a mixture can vary.

JOSEPH-LOUIS PROUST
French chemist Joseph-Louis
Proust (1754-1826) liked to analyse
the content of anything that came
within his reach. He discovered
that the proportions of elements
in any compound was always
the same. This went against the
thinking of respected scientists,
but Proust was proved right.

He had discovered the law
of constant composition.

LAW OF CONSTANT
COMPOSITION
Salt (sodium chloride, NaCl)
is a compound that is found
in sea water, salt mines, or
can be made in a laboratory.
But it is always the same salt,
containing one sodium
atom to one chlorine atom.
A pure compound always
contains the same elements in
the same proportions.

Plastics are compounds of mostly
hydrogen and

carbon. ^ _1

There are compounds
and mixtures everywhere
in this city scene from
Florida, U.S.A.

Glass is a
compound of
silicon and
oxygen.

Car bodies are
made using
mixtures of metals,
called alloys.

Types of mixture

Solids, liquids, and gases
can all be mixed in
different combinations.
Liquid mixtures, for
example, are found in
several forms. Alcohol
and water mix easily.

They are miscible liquids.
Immiscible liquids such as
vinegar and oil separate
into two parts. By adding
a substance called an
emulsifier, the oil droplets
will float suspended in the
vinegar to produce a
mixture called an
emulsion. Mayonnaise is
an emulsion of oil in
vinegar. The emulsifier
used is egg yolk.

Incense smoke is a
mixture of
and
air.

Bread is a
mixture of a
solid and a gas. m

Shaving

foam

is a

mixture

of a liquid

and a gas.

Fizzy
drinks
have a gas, carbon
dioxide, dissolved in
the liquid.

SYNTHESIS AND DECOMPOSITION
Chemists often build bigger and more
useful molecules from smaller ones.
This is called synthesis. Sometimes it is
necessary to do the opposite and break
down the larger molecules into smaller
ones. This is called decomposition.

In salad dressing,
oil floats on top of
vinegar. These
two liquids will
not mix. They
are immiscible.

Whisky is a mixture
of two miscible
liquids, alcohol
and water, which
is why it does not
separate into two parts.

Hair gel is a mixture of a
solid, fat, and water. The fat
traps the water and stops it
from moving around.

When flour is mixed
into water, it stays
suspended in the
water. Flour and water
form a suspension. A
colloid is a suspension
in which the suspended
particles are very tiny.

Sodium is a
highly reactive,
silvery-grey
metal.

In an alloy, atoms
of one metal stop
those of another
from sliding
around.

ALLOYS

Objects such as
spacecraft must
be made of light
yet strong material.

Pure metals are not
tough enough and so
mixtures of metals,
called alloys, are
used. Alloys are made
by adding a small
amount of one pure
metal to another. As the atoms of
the second metal are
different in shape,
they change the
formation of the
original metal.
This makes it
tougher and
more difficult
to bend.

This space shuttle is
made of a titanium alloy.

Chlorine is a
poisonous
green gas.

When sodium and
chlorine combine, they
make sodium chloride,
or common salt.

DIFFERENT COMPOUNDS
Copper and oxygen can make two
different compounds. Copper
(I) oxide, a red-brown powder
has two parts of copper to
one part of oxygen.

Copper (II) oxide
has one part
of copper to
one part of
oxygen and
is grey-black.

Copper (I) oxide
(Cu 2 0)

Making a
compound

Compounds are
very different from
the elements which
make them. Common
salt is a compound of

sodium and chlorine. Sodium is a metal that is
stored in oil as it reacts dangerously with air or water.
Chlorine, a reactive green gas, is poisonous in large
quantities. When sodium and chlorine atoms join,
they lose their dangerous and poisonous properties.
They form a new compound, .sodium chloride, which
is the familiar salt that we use to flavour our food.

Copper (II) oxide
(CuO)

MOVING ELECTRONS
Atoms are made of a nucleus with
electrons moving around it in different
levels or shells. An atom is generally most
stable if it has eight electrons in its outer
shell. If it has fewer than this, the atom is
reactive and may be dangerous. When
sodium and chlorine combine, electrons
move places so that both sodium and
chlorine each have a stable outer shell
of electrons and the compound they
make, salt, is stable and unreactive.

A sodium atom gives one
electron to a chlorine atom so
that each ends up with eight
electrons in their outer shell.

Electron

Chlorine

atom

PURITY

In chemical terms, pure substances
contain only one type of atom or
molecule. Pure gold is made up of gold
atoms and nothing else. Some drinks
are described as “pure juice”, which
means that nothing artificial has
been added to them. To a chemist,
however, the juice is not a pure
substance as it is a mixture of
compounds like water and
sugar. Mixtures are not pure,
unlike compounds, which con
only one kind of molecule.

Although freshly squeezed orange juice
contains no additives, a chemist would
not call it pure as it
is made of more
than one kind
of molecule.

carat

Only 24 carat
gold is pure gold.
Lower carats of
gold are mixtures
of gold with other,
cheaper metals.

9 carat gold
contains only
37% gold.

Find out more

Atomic structure p.24
Bonding p.28
Elements p.31
Chemical reactions p.52
Solutions p.60
Separating mixtures p.61
Chemical analysis p.62
Alloys p.88
Cosmetics p.103

REACTIONS

SATURATED SOLUTION
The Dead Sea between Israel and
Jordan contains a massive amount of
salt. The water evaporates in the hot
Sun, leaving the same amount of salt
but less water. There is no longer any
room for all the dissolved salt, and it
forms solid crystals. When solutions
cannot hold any more solute, they
are said to have become saturated.

INSOLUBLE SOLIDS

Substances that dissolve in water, such as salt, are said to be
soluble in water. Insoluble substances, such as sand and oil,
will not dissolve. This is because the water cannot overcome
the forces holding the molecules of sand or oil together.
These molecules prefer to stay bonded to each other,
rather than separate and mix with the water molecules.

Solutions

A f izzy
fruit drink is a
solution
of fruit juice,
sugar, and carbon dioxide.

.SeA WATER LOOKS CLEAR, but it contains many
substances, such as salt and oxygen, which have dissolved
in the water and become invisible. It is an example of a
solution, a special type of mixture in which different
molecules are evenly mixed. Solutions are often made by
dissolving a solid into a liquid, like when sugar is stirred into
tea. Sugar is called the solute and tea is called the solvent.
There are other kinds of solutions too. Gases, liquids, and
solids can all be solutes or solvents. Concentrated solutions
contain a large amount of solute in a solvent, while in
dilute solutions there is only a little solute. Orange squash
is a concentrated solution that is diluted by adding water.

Tube
of glue

Solvent

molecule

Adhesive

molecule

When glue dries, the
solvent evaporates,
leaving the reactive adhesive
^ q e molecules to link up.

ion is attracted to
the negative end
of a water
molecule.

Attracting molecules

Whether a substance will A positively charged
dissolve depends on how
much the molecules of
solute and solvent are
attracted to each other.

Water is a good solvent
as it has a slight
electric charge and
can form weak bonds
with other charged
particles. Certain
compounds, such as salt,
break down in water into two
particles, one with a positive
charge and one with a negative
charge. These particles, called ions, can
form weak bonds with the water molecules.

Fish use the small amounts of oxygen dissolved in water
to stay alive. Unlike solids, gases dissolved in liquids
come out of solution when the liquid is heated. This is
one reason why fish cannot survive in very warm water

NON-LIQUID SOLUTIONS
Air is a solution of oxygen and other gases
dissolved in nitrogen. Boats are made from
alloys that are solid solutions of one metal
dissolved in another metal.

Water

molecule

Water

molecule

4,0

e • <a©

Dissolved
particles
mix with
water
molecules.

DIFFERENT SOLVENTS
Some substances will not dissolve in
water. Some types of glue, for example,
have to be dissolved in another type of
solvent called an organic solvent, such
as acetone. When glue dries, the solvent
evaporates, leaving behind the sticky
solid that binds the surfaces together.

The air that deep-sea divers breathe
dissolves in their blood to form a solution.

If the diver surfaces too quickly, the air
can come out of solution to form bubbles
in the blood. This is a dangerous condition
_ _— known as ‘the bends”.

UNIVERSAL SOLVENT

Alchemists were early chemists. In
the course of their experiments,
they discovered ways to purify metals
by dissolving them in solvents. The
alchemists dedicated themselves to
the search for a “universal solvent”,
a substance in which all things would
dissolve. They never found it. If they
had, what would they have kept it in?

- Find out more -

Properties of matter p.22
Bonding p.28
Organic chemistry p.41
Compounds and
mixtures P.58
Separating mixtures p.61
Chemistry of water p.75
Adhesives p.106

REACTIONS

When you cook rice

you use a sieve to separate
the rice from the water, a method known as filtration.
Chemists use this and other familiar techniques to
separate mixtures in a laboratory so that they can study
one particular substance. The method they choose
depends on the type of mixture and the different
properties of the substances it contains. For example,
since tea leaves do not dissolve in tea, you can use a
strainer to filter them. If the tea leaves were fairly large,
you might just leave them to settle before drinking the
tea. This is another technique known

Substance
to be kept dry

\ Silica gel

DESICCATION
To keep substances dry in the
laboratory, chemists might put
them in a desiccator. This sealed
dish contains a solid, such as silica
gel, that absorbs the moisture in
the air. Packets of silica gel are
often put inside camera cases so
that moisture will not ruin the
lens. Desiccation is simply a
separating technique that
removes water from a solid.

DECANTING

To search for gold in rivers,
huge pans were once used to
scoop up a mixture of sand,
gravel, and river water. The
mixture was swirled around,
and any heavy gold particles
sank to the bottom. The
unwanted muddy liquid could
then be decanted (poured)
off. Decanting separates two
substances with different
densities. As cream is less dense
than milk, for example, it
can easily be decanted off.

Only the water can fit through the
holes in the filter paper. The coffee
ground particles are too large.

Water particle

Coffee ground
particle

Filtration \\ jm

In a coffee maker, a filter is

used to separate the ground beans vf?!

from the liquid coffee. As the water runs over the
grounds, the coffee dissolves in the liquid and passes ^
through the tiny holes in the filter paper. The grounds
are too large to pass through the filter, and so are left
behind. To separate a mixture by filtration, the different
parts of the mixture must be present in different-sized pieces.

Centrifuge

DISTILLATION
If you were marooned on a desert island, how
would you obtain pure water to drink? If sea water
is boiled, the water comes off as steam. If this is
then cooled, pure liquid water can be collected.
This is a separating method called distillation that
is used whenever the liquid part of a mixture is
needed. The method can also be used if a
mixture of liquids needs to be separated. This is
fractional distillation. By heating the mixture, the
liquid with the lowest boiling point will come off
first. The liquid fraction with the
7/Vo, highest boiling point will

\ come off last.

As the tubes
are spun,
the heavy
particles
sink to the
bottom.

Drying crops in the Sun

CENTRIFUGING
A centrifuge is like a spin-dryer.

It separates
mixtures of liquids and solids by spinning
them around at high speed. Dense
substances sink to the bottom, while the
less dense substances rise to the top. Test
tubes of blood are centrifuged to separate
the heavier blood cells from liquid plasma.

Find out more

/k Cooling
v water out

EVAPORATION
Fruit such as grapes can be left
outside to dry in the Sun. The heat
turns the liquid water in grapes into
water vapour which is lost to the air,
leaving wrinkled sultanas. This
process of removing a liquid by heat
is known as evaporation. Drying
your hair with a hair drier is another
example of evaporation.

Changes of state p.20
Properties of matter p.22
Compounds and

MIXTURES P.58

Solutions p.60
Chemical analysis p.62
Oil products p.98
Circular motion p.125

Cooling
water in

The heat turns a
S pure liquid component
of the mixture
into a gas.

The mixture is
heated in a flask.

6 .

When the gas is
cooled, it turns to a
liquid and is collected.

Separating mixtures

REACTIONS

Chemical analysis

CHEMISTS OFTEN WORK like detectives. They look for
clues to reveal the true identity of a substance. Food
chemists carry out experiments to find whether food
contains poisons or bacteria. Medical chemists examine
fluids such as blood and urine for signs of disease in our
bodies. Environmental chemists measure the health of the
environment by testing samples of air, water, and soil, so
that they can record levels of pollution. Scientists can use
a wide range of techniques to analyse substances.

Identifying the ingredients of a substance is called
qualitative analysis. Finding out exactly how much of
each ingredient it contains is called quantitative analysis.

The test
solution turns
from colourless
to pink when it
has all reacted.

GAS CHROMATOGRAPHY
To separate a mixture of gases, chemists
sometimes use a technique called gas
chromatography. The mixture is made to
travel through a solid, and because some
parts of the mixture are more strongly
held by the solid than others, the
mixture is separated into its components.

Solution
of known
concen¬
tration

FORENSIC SCIENCE
Forensic scientists use many tests to
solve crimes. One technique called
genetic fingerprinting, which is similar
to chromatography, is used to find out
if a sample of blood or other body
tissue, found at the scene of a crime,
came from a particular person. Tiny
fragments of genetic material (DNA)
from the sample of tissue are separated
according to their mass, using
electricity. The resulting pattern, which
looks like a supermarket bar code, is
called a DNA fingerprint. It is
compared with a suspect’s own DNA
fingerprint, to help solve the crime.

DESTRUCTIVE TESTING
Real gold or fool’s gold? Fool’s gold
is a compound of iron and sulphur
that looks like gold. To test a sample,
chemists can weigh it (fool’s gold is
lighter), drop acid onto it (fool’s
gold will dissolve), or drag it across a
white tile (fool’s gold leaves a black
streak). The acid test and the white
tile test damage the sample. They are
destructive testing methods. Non¬
destructive testing, such as weighing,
leaves the sample intact.

TITRATION

To find out the concentration of a
solution, chemists use a method
called titration. They make the
solution react with a chemical
whose concentration is known.
When all of the solution has
reacted, a colour change occurs.
Its concentration can then be
worked out by measuring how
much of the chemical was used.

Everyone except
identical twins has a
DNA fingerprint that
is unique to them.

Chromatography

Black ink may be a mixture of different dyes.
When you put a drop onto filter paper and then
add water, the blot spreads out into different
coloured rings. Each separate ring contains a
different dye. The dyes separate because some
stick to the paper, and so remain near the
centre, while others stay dissolved in the water
and are taken farther out. This is a technique
known as chromatography. Chemists often use
chromatography to test a substance for purity,
and doctors use it to analyse urine samples for
traces of sugar (which would indicate diabetes).

Fool's gold

When fool’s
gold is dragged
across a white
tile, it leaves a
black trail. Real
gold leaves
no mark.

The blue dye stays near to the
centre of the paper because it is
more attracted to the paper
than the other dyes.

The yellow dye travels on to the
edge of the paper as it is more
attracted to the water
than the other dyes.

Scientists, like cooks, need weighing
scales so that they can make
accurate measurements of the
substances they use in the
laboratory. This is a type
of quantitative analysis.

REACTIONS

Ions with a \
small mass are \
deflected too far to
be picked up by the
detector. Ions with a
large mass are
not deflected enough.

The stream
of ions is
speeded up
by an electric field
and then deflected
(made to alter
its direction) by
a magnetic field.

Detector

Only one type of ion is

FRANCIS ASTON

English chemist Francis William
Aston (1877-1945) invented the
mass spectrometer in 1919.

Aston worked as assistant to
J. J. Thomson at the Cavendish
Laboratory, Cambridge
University, where he studied
positively charged rays. The
invention of the mass
spectrometer led Aston to
discover many new isotopes. This
work won him the Nobel Prize for
Chemistry in 1922.

MASS SPECTROMETER

Although the masses of atoms are too small to be
measured, they can be compared. A very accurate
piece of equipment that does just this is the
mass spectrometer. It separates the atoms in
a sample according to their mass and shows
the amounts of the different atoms that
are present. It does this by turning the
atoms into ions and deflecting them in
a magnetic field. Heavier ions are
deflected more than light ones.

The ions are therefore separated
and can be identified.

Reading from
mass spectrometer

The sample is turned into
a gas, and its atoms are
converted into ions.

Sodium compounds
burn with an
orange flame.

Environmental chemist
testing the purity of a river

deflected by the right amount.
By changing the strength of the
magnetic field, different ions
are recorded by the detector.

Atomic emission spectrum
of the element helium

Lead compounds
burn with a

blue flame.

The height of the peak
gives the number of
each ion present.

The bottom scale gives
the mass of each ion.

ATOMIC EMISSION SPECTRUM
The coloured light given out, or
emitted, by an atom during a
flame test is only part of the story.

The atom actually emits a whole
range of different lights when it is
heated, but only some light is
visible to us. The other frequencies
of light can be picked up by an instrument called
a spectroscope to give the atomic emission
spectrum. This is the fingerprint of an atom.
Each element has a different spectrum.

Copper compounds burn
with a green-blue flame.

Flame tests

When a metal compound is
heated in a flame, it burns to
give the flame a particular
colour. This happens because
the heat of the flame makes the
electrons in the atom move
around, and as they do so they give off light. Different
metals give different colours of light to the flame and
so this colour identifies the metal. Copper compounds,
for example, always give a green-blue colour to a flame.
These characteristic colours of metal compounds are
also responsible for the beautiful colours of fireworks.

Barium compounds
burn with a
brown-green flame.

Potassium
compounds burn
with a lilac flame.

WATER TESTING
Environmental scientists use
chemical analysis to test the
quality and safety of water. A
river may be polluted with
fertilizers, detergents, waste,
sewage, or acid rain. A scientist
can use titration methods, for
example, to find out how
much of a dissolved substance
a sample of water contains.

ANALYSING NAPOLEON

After his death, chemists analysed
hair samples from the French
emperor Napoleon
Bonaparte (1769-1821)
and found traces of arsenic,
a poison. Murder was
suspected. But recently it
was discovered that the
colouring in his wallpaper
contained high levels of
arsenic. Dampness and mould
may have turned it into a deadly gas.

Lithium compounds
burn with a
red flame.

Find out more

Atomic structure p.24
Compounds and

MIXTURES P.58

Separating mixtures p.61
Sources of light p. 193
Genetics p.364
Factfinder p.404

REACTIONS

Oxidation and reduction

Every time
something
bums, it
combines with
oxygen from
the air. Burning
is an oxidation
reaction.

If YOU FELT COLD ON THE MOON, you would never be
able to light a fire to keep warm. This is because burning is a
reaction in which a substance combines with oxygen - an
oxidation reaction - and there is no oxygen around the
Moon. Many important, everyday chemical reactions involve
oxidation. It occurs when substances burn, when metals rust,
and even when we breathe. The food that we eat is converted
into energy by combining with the oxygen that we breathe in.
Substances that combine with oxygen or that lose hydrogen
are said to be oxidized. The process where a substance loses
oxygen or gains hydrogen is called reduction, and it always
happens at the same time as oxidation: when one substance
gains oxygen, another must give it up.

This molecule is an oxidizing agent, as
it is giving oxygen to another molecule.

REDUCTION

When a substance loses oxygen or gains
hydrogen in a chemical reaction
it is reduced. This is caused by
another substance removing
oxygen or giving hydrogen. This
other substance is known as a
reducing agent. One example of
this is the gas carbon monoxide
given out by car exhausts. This
will readily gobble up oxygen to
form carbon dioxide.

This molecule has been reduced.

It has gained a hydrogen atom.

This molecule is a reducing agent, as it is
giving hydrogen to another molecule.

OXIDATION
When a substance gains
oxygen or loses hydrogen in a
chemical reaction, it is
oxidized. Oxidizing agents are
substances that give oxygen
to, or accept hydrogen from,
another substance. Familiar
examples are the air and
bleach - both have a high
oxygen content.

This molecule has been oxidized.

It has gained an oxygen atom.

Rusting

If iron or steel are exposed to air and
moisture, they will rust. Rusting is a
destructive example of an oxidation
reaction. The iron is oxidized to form
iron oxide (rust). Once the top layer
of metal has rusted, oxygen from the
air can reach the inner layers. Rust will
therefore quickly eat its way through the
metal. Applying a coat of protective paint to
a surface such as the hull of a ship prevents
rust from forming, because the oxygen in the
air cannot reach the iron.

OXIDES

When non-metals combine
with oxygen, they form oxides
which make acid solutions in
water. Nitrogen oxide and
sulphur dioxide, for example,
are non-metal oxides produced
by power stations. When these
oxides dissolve in the moist air,
they fall as acid rain, harming
trees, lakes, and buildings. This
is why power stations are now
trying to control their
emissions. Metals, on the other
hand, combine with oxygen to
form oxides which make
alkaline solutions in water.

OXIDATION IN KILNS
Potters may put a glaze on
their pots that contains a metal
- iron, for example. When the
pot is baked in a kiln
containing a lot of oxygen, the
iron is oxidized to one form of
iron oxide, Fe^Og, which is
red. If the pot is baked in a kiln
containing only a little oxygen,
another form of iron oxide, FeO, is
formed, which is black.

PHLOGISTON THEORY

Watching flames leaping from wood
inspired a German doctor, Georg
Stahl (1660-1734). He
suggested that everything that
burned gave out a substance
called phlogiston. Later,
Antoine Lavoisier (1743-94),
a French chemist, dismissed
this theory. He proved that

when something burns, it
combines with oxygen from the air.

ELECTRON TRANSFER
During the oxidation and reduction
processes, there is always a movement
of electrons between the atoms.

Atoms that gain electrons are said to
be reduced. Atoms that lose electrons
are said to be oxidized. Nowadays,
chemists call these processes oxidation
and reduction, even when oxygen and
hydrogen are not involved in the reaction.

This atom is
being oxidized.

This atom is
being reduced.

REACTIONS

Hydrogen

atom

Carbon

atom

MAKING MARGARINE
The margarine that you spread
on your bread is made from
liquid vegetable oils, such as
sunflower oil. To turn these
liquids into solid fats, the oil
is combined with hydrogen.
This process is called
hydrogenation and is an
example of a reduction
reaction. By controlling H

the amount of jp

hydrogen added to /CjjjJ
the oils, the
margarine can be
made as sof t or as
hard as needed.

Molecule of

hydrogen

gas

w Portion
of oil
molecule

The liquid oil
molecule has been
reduced, because
hydrogen has
been added
to it. This
process turns
the liquid oil
into a solid.

GUNPOWDER

Gunpowder was

discovered

accidentally by

Chinese alchemists

in the 7th century. Its

main ingredients are saltpetre

(potassium nitrate), sulphur, and carbon. Setting

to gunpowder is an example of an explosive oxid

fuost substances burn by taking oxygen f rom the

Portion of
molecule
in solid fat

ANTIOXIDANTS
Food can go
bad by reacting
with oxygen in

prevent this,
chemicals called

antioxidants are added to the food when it is made.
It is these, rather than the food, which will react
with the oxygen and so the food is kept fresh.
Antioxidants are often found in fatty foods such as
vegetable oils because fats are very quick to oxidize.

Exhaust

gases

The petrol and air are
compressed and
exploded by an electric
spark. The hot gases
that are produced
force the piston down.

Internal

combustion

engine

Petrol vapour
and air are
mixed together
and sucked into
the cylinder.

As the
piston rises,
the hot gases
are pushed out
of the cylinder
and into the
car exhaust.
The cycle is
then repeated
over and over
again.

FIRE-FIGHTING
To burn, a fire needs a fuel
(the burning substance)
and heat. Since burning is an
mfr oxidation reaction, a fire also
needs a supply of oxygen to
keep going and by taking this
Bk away, the fire can be stopped.
This can be done either by
smothering the flames with a
B blanket, or by covering them
with foam or carbon dioxide
W" f rom an extinguisher.

Combustion

Combustion means
burning. Inside an
internal combustion ^
engine of a car, petrol B|
is burned to release
the energy which the
car needs to move.

Like all burning L -

reactions, this is an
example of an oxidation
reaction. Petrol combines
with oxygen, and this
reaction releases energy.

Piston

The movement of the
piston in the cylinder
provides the power
to make the
car move.

BREATHALYSER
Police officers often use an oxidation reaction
to test for drunk drivers. When someone
breathes into a breathalyser, any alcohol
(ethanol) in their breath is oxidized to make
ethanoic acid. This produces an electric
current. The strength of the current shows the
amount of alcohol present in the driver’s breath.

\Ne take in the
oxygen given out by
plants and use it to
oxidize the food we
eat. This reaction
gives us energy.

RESPIRATION AND PHOTOSYNTHESIS
Two life-giving reactions called
k respiration and photosynthesis

^ are oxidation and

Plants reduce the reduction reactions. In
carbon dioxide we respiration, the food
^ breathe out to we eat - ls oxidized. This
v °° S releases the energy our

'f ^ oxygen bodies need. Plants

use a reaction called
^ Ah, photosynthesis to reduce

carbon dioxide from the
air to form sugars and starches.

Plants release
oxygen by
photosynthesis

BLEACHING

Household bleaching fluids
contain powerful oxidizing
agents that oxidize the
coloured substances in cloth
and make them colourless.
Modern bleaches contain
hydrogen peroxide, ^C^-
Its formula shows that it
contains a lot of oxygen.

Find out more

Atomic structure p.24
Oxygen p.44
Hydrogen p.47
Chemical reactions p.52
Chemistry of air p.74
Engines p.143
Photosynthesis p.340
Cellular respiration p.346
Fact ftnber p.404

REACTIONS

Copper
- metal

Reactivity series

Potassium IS SO REACTIVE that it is rarely found on its
own. It is usually tightly bonded to other elements. Silver, on
the other hand, is such a remarkably unreactive element
that it can be safely used for cutlery, because it will not
react with food. By comparing the way they react, a table
of metals can be drawn up. This is called the reactivity
series.The metals at the top of the series are the most
reactive; the metals at the bottom are the least reactive.

The series is used to predict what will happen when different
metals react together. For example, if potassium and silver
were competing to react with chlorine, potassium would win
and potassium chloride would be formed. A metal will win any unreactive gold
competition between it and another metal lower in the series, discover gold objects, such as

Silver metal collecting

Displacement

When copper is dropped into a
solution of silver nitrate, the two
metals compete for the nitrate ions.

Because copper is higher in the
reactivity series, it is able to “grab”
the nitrate ions from the silver. The
result is a blue solution of copper
nitrate and needles of silver metal.

This is called a displacement
reaction, as the copper metal has
displaced the silver from solution.

If aluminum's oxide layer is removed, the
exposed aluminum reacts violently with air.

jewelry or masks. These are
often as good as new, even
though they have been
buried for thousands of years.
Unlike most metals, which
would have corroded, gold is
an unreactive metal. This is
why it is placed at the bottom
of the reactivity series.

I \

; ^ '

- Copper
metal

Ag+

Blue solution
of copper
nitrate forming

Silver in
solution

The silver and the
copper have
swapped positions.

ALUMINUM

Aluminum is an odd metal. It is high
in the reactivity series, and yet
aluminum saucepans are used to
cook food. This is because it reacts
with oxygen in the air to form a
protective layer of aluminum oxide.
But if this layer is broken down, for
example, by rubbing aluminum foil
with a chemical called mercury
chloride, the exposed aluminum is
extremely reactive.

HISTORY OF METALS

The use of metals came
late in history. Early
people used only bones,
stone, and wood. Since
copper, silver, and gold
are at the bottom of the
reactivity series, they were
easily found, and were the
first metals ever used. By
2000 B.C., iron, a more
reactive metal, could be
extracted from its ores by
heat. The Iron Age had
begun. Aluminum is a
common but very reactive
metal that could not be
extracted until the

19th century. Iron tongs from

7 the Iron Age

Potassium

Sodium

THE SERIES
This is the
reactivity series.

It shows the
order of
reactivity
of different
metals. Those
at the top, such
as sodium and
potassium, react
violently with air.
Those at the bottom,
such as silver and
gold, are unaf fected
by air. Those in
between, such as iron
and zinc, react slowly.
The way a metal is
extracted from its ores
(naturally occurring
compounds) depends
on its position in the
reactivity series.

Calcium

Magnesium

Aluminum

Platinum

Gold

Sodium is high
in the reactivity
w series, and it

.. » forms very stable

compounds.
\ Aj Sodium metal has
to be obtained from
molten sodium
chloride by the
powerful but
expensive method
of electrolysis.

Copper is lower
down the reactivity
series, so less
energy is needed
to extract it.
Copper can be
obtained by
just heating
its ores.

Gold, at the bottom
of the reactivity
series, is
unreactive
and can be
%j0found uncombined
in nature.

GALVANIZING
Objects made of steel, which is
mostly iron, can be protected
against rusting by a coating of a
more reactive metal, usually zinc.
This process is called galvanizing.
Oxygen in the air will react with
the zinc, rather than with the iron,
even if the zinc layer is scratched.
This is sometimes called sacrificial
protection, since the zinc has
been sacrificed to protect the iron.

Find out more

Alkali metals p.34
Transition metals p.36
Solutions p.60
Electrol\sis p.67
Iron and steel p.84
Copper p.86
Aluminum p.87
Fact finder p.404

REACTIONS

Electrolysis

X Instead of using

/ electricity to produce
r chemical reactions, chemical
reactions are able to generate ,
electricity. This happen^
in a battery

Copper f

sulfate I

solution I

Pure

copper

metal

Breaking a compound apart using electricity is a

process called electrolysis. For this to work, the compound
has to conduct electricity - it must be molten or in solution,
and it must contain electrically charged ions that are free
to move. Two metal or carbon rods, (the electrodes),
are placed in the substance to be split (the
electrolyte). When a battery is connected,
electricity flows through the liquid. The positive
ions of the compound move to the negatively
charged electrode (the cathode). The negative
ions move to the positively charged electrode
(the anode). The compound is split into two parts.

ANODIZING

If electricity is passed through acid
with aluminum as the anode, oxygen
is formed at this anode and reacts with
the aluminum to form a protective
coating of aluminum oxide. This is
called anodizing. Colored foils are
made by dyeing this oxide layer.

Hydroxide ion

Moving ions

When electricity is passed
through a solution of
potassium chloride (KC1)
in water (H 2 0), not only
is the potassium chloride
pulled apart, but also the
water. The potassium ions
and hydrogen ions, both
positively charged, move to the
cathode but, because potassium “prefers” to
stay as an ion, it stays in solution, and only
hydrogen gas is given off. Chloride ions and
hydroxide ions, both negatively charged,
move to the anode. The hydroxide ions stay
in solution, and only chlorine gas is given off.

Anode

Cathode

Hydrogen ion
Potassium ion

Potassium hydroxide is
left in the container.

ELECTROREFINING
Electrolysis can be used to purify
copper. This process is called
electrorefining. Impure copper is
the anode, a sheet of pure copper
is the cathode, and the electrolyte
is copper sulfate solution. When
electricity is passed through the
solution, pure copper is
transferred from the impure to
the pure sample. The impurities
fall to the bottom of the solution.

Key before
electroplating

Key after
electroplating
(coated with
copper). _

At the
cathode,
positively
charged hydrogen ions take
electrons to form hydrogen
atoms, which join up to make
hydrogen gas.

Battery

At the anode,
negatively
charged
chloride ions
give up their
extra electrons
to form chlorine
atoms, which join up to
make chlorine gas.

HUMPHRY DAVY

The English chemist Humphry Davy
(1778-1829) is best known for his
invention of the miner’s safety lamp,
but he was also one of the first to use
electrolysis. He discovered sodium,
potassium, calcium, and a number of
other metals because he
was able to separate
them from their
compounds by
electrolysis. Davy
appointed an
assistant called
Michael Faraday in
1813, who
continued Davy’s
work and went
on to become a
very famous
scientist himself.

WATER

When electricity is passed
through water (H 2 0),
hydrogen gas forms at the
cathode and oxygen at the
anode. Because water
contains two hydrogen
atoms for every oxygen atom,
twice as much hydrogen as
oxygen is produced.

ELECTROPLATING u

Coating an object, like a key,
with a thin layer of metal is a
process called electroplating.
The object is made the
cathode. The anode is a pure
piece of plating metal, such
as copper. The electrolyte
contains a compound of this
metal (copper sulfate, for
example). Metal ions move
through the solution and coat
the object. Tin cans are made
by electroplating tin onto steel.

__ Hydrogen

gas

Oxygen
gas

The key must be rotated so
that it gets an even plating.

I ^

Water
Electrode

^ Battery

Find out more

Bonding p.28
Solutions p.60
Reactivity series p.66
Copper p.86

Cells and batteries p.150
Fact finder p.404

REACTIONS

Scientists use the pH scale to describe the strength of acids and
alkalis. It runs from 1 to 14. The more hydrogen ions it contains, the
stronger it is, and the lower its pH. All acids have a pH of less than 7.

Acids

Acid half of the pH scale

A LEMON TASTES SOUR because it contains an
acid called citric acid. In fact, the word acid means
“sour” in Latin. Acids are everywhere. They are
found in ants (methanoic acid), grapes (tartaric
acid), fizzy drinks (carbonic acid), car batteries
(sulphuric acid), and even in our stomachs (hydrochloric
acid). Strong acids such as sulphuric and nitric acids, which
are used in laboratories, are very dangerous and will burn
clothes or skin. Some weak acids, such as those found in
fruits, are safe to eat. All acids contain hydrogen and
dissolve in water to form positively charged hydrogen ions.
| It is these ions that give acids their special properties. The
number of hydrogen ions an acid can form in water is a
i measure of its strength, known as its pH.

Positive
hydrogen ion

HIGH pH
Citrus fruits such as
lemons and oranges
contain citric acid. This is
a weak acid. It has a fairly
high pH, but still under 7.

Negative ion

STRONG ACIDS

Some acids, such as nitric acid and sulphuric acid,
are strong. Their molecules completely dissociate
(split up) into hydrogen and other ions in water.
The strength of an acid tells us how many of these
split-off hydrogen ions are present in the solution.
Just as you dilute orange squash with water, you
can dilute strong acids with water, so there are
fewer hydrogen ions in solution. This lowers their
acidity (increasing the pH).

Concentrated strong acid

Dilute strong acid

LOW pH

Acids found in the laboratory,
such as sulphuric acid, are
strong. They have a low pH. We
have a strong acid, hydrochloric
acid, in our stomachs to help
digest our food.

WEAK ACIDS

Some acids, such as the citric acid found in
oranges and lemons, are weak acids. When
dissolved in water, only a very small number of
their molecules will dissociate to form hydrogen
ions. You can make concentrated or dilute
solutions of a weak acid by either removing or
adding water. A very concentrated solution of a
weak acid and a very dilute solution of a strong
acid may well have the same pH.

ACID FROM ANTS

An acid called methanoic acid (formic acid) is
produced naturally by both stinging ants and
stinging nettles. Long ago, people made
formic acid by boiling ants in a big pot.
Today, it is made from other chemicals. It is
used to preserve silage (crops stored for
animal fodder) and to make paper and textiles.

Lead-acid battery

Strong acids make good
electrolytes (liquids that conduct
electricity). This is because in
water they are almost completely
split up into positive hydrogen
ions and negative ions. These
electrically charged ions can carry
an electric current. Sulphuric acid
is used as the electrolyte in the
lead-acid batteries found in cars.
Lead plates act as the electrodes.
These batteries produce the
energy to start the car.

A clam will die if A salamander will
the pH of its water die if the pH of its
falls below 6. water falls below 5.

AGID WATER
Lakes and rivers can be
polluted by acid rain. This
increases the acidity, or lowers
the pH of the water, and so
may be harmf ul to fish and
other aquatic life. Some
animals are more sensitive to
these pH changes than others.
A clam, for example, cannot
survive if the pH of its water
falls below 6. Wood frogs, on
the other hand, can survive in
water with a pH as low as 4.

Sulphuric
acid electrolyte

A brook trout will die A wood frog will
if the pH of its water die if the pH of its
falls below 4.5. water falls below 4.

Negative

lead

electrode

Positive

lead

oxide

electrode

Positive
hydrogen ion

P „©

Negative ion /

e © •

v o . (r

6 P

Concentrated weak acid Dilute weak acid

REACTIONS

The cork flies out of the ^
bottle. It is pushed by
the carbon dioxide gas
created during the
chemical reaction
between the vinegar and
the bicarbonate of soda.

ACID ON PAPER
Concentrated sulphuric acid is very corrosive. It
acts as a dehydrating agent, which means that it
removes water from any substance it comes into
contact with. Paper is made from cellulose, a
plant material that contains carbon, hydrogen,
and oxygen. When sulphuric acid reacts with
paper, it removes the water (hydrogen and
oxygen), and leaves the black carbon behind.

This is why the paper looks burnt.

A furious
bubbling of
hydrogen gas
is given off.

Hydrochloric

acid

Chippings of
zinc metal

Vinegar
mixed with
bicarbonate
of soda

A compound called sodium
ethanoate is left behind in
the bottle. This is a salt.

ACID ON METAL

You should never store vinegar in a metal
bottle. It can create a slight fizzing of
hydrogen gas. The hydrogen that all acids
contain can be driven off when the acid
meets a reactive metal. This is why acids
are never kept in metal containers. When
hydrochloric acid is poured on zinc
(above), there is a fizzing of hydrogen
gas. The zinc replaces the hydrogen in
the acid to form zinc chloride.

ACID DISCOVERIES

11th century Arabic chemists find
out how to make sulphuric, nitric,
and hydrochloric acids.

1675 Irish chemist Robert Boyle
wrongly suggests that acids contain
special particles that squeeze into
gaps in metals, breaking them apart.

1854 The writing of French chemist
Auguste Laurent proves that all
acids contain hydrogen.

1887 Swedish chemist Svante
Arrhenius proposes that all acids
contain hydrogen ions and these
give acids their special properties.

YELLOWING PAGES
Have you noticed that the pages in
new books look very while, while
those in older books have turned
yellow? Paper contains tiny amounts
of an acid. Over years and years,
this acid very slowly starts to break
down the cellulose fibres in the
paper. This changes the colour of
the paper from white to yellow. The
reaction is speeded up by sunlight,
and the paper may turn brown and
become brittle.

Acid on carbonate

If you add vinegar (ethanoic acid)
to bicarbonate of soda (sodium
hydrogen carbonate) in a corked
bottle, a fizzy reaction occurs. The
acid breaks down the carbonate to
make carbon dioxide gas. So
much gas is produced that it fills
up the bottle, and then forces the
cork out like a cannonball. Acids
will always break down carbonates
to form carbon dioxide. This
reaction is used in cookery.
Baking powder is a mixture of
cream of tartar (a form of
tartaric acid) and bicarbonate
of soda. In water, they make
carbon dioxide, which is the
gas that makes cakes rise.

WARNING SYMBOL
Although acids often look like water,
strong acids are corrosive and
cause severe burns. Because of
this, the containers in which acids
are transported carry a hazard
warning sign. This has a code that
identifies the acid and tells the fire
brigade how to deal with a spillage.

ACID IN RAIN

Rainwater has always been slightly acidic,
as carbon dioxide in the air dissolves in
rain to form carbonic acid. But the
acidity of rain has increased since the
world became industrialized. This is
because fossil fuels such as coal release
sulphur dioxide and nitrogen dioxide
when they are burned. These gases react
with the water in clouds to form
sulphuric acid and nitric acid. Acid
rain threatens many buildings,
especially those made of limestone,
which is calcium carbonate. This is
because acids easily break down
carbonates into carbon dioxide gas.

PICKLING
Since acids are
dangerous to
living things, they
can be used as
preservatives to
kill bacteria. Many
foods, like onions
and beetroot, are
preserved by
soaking in
vinegar
(ethanoic acid).
This process is
called pickling. The acid kills any
micro-organisms and so stops the food
going bad. Pickling was widely used
before the invention of refrigerators.

Find out more

Bonding p.28
Hydrogen p.47
Solutions p.60
Alkalis and bases p.70
Measuring acidity p.72
Salts p.73

Sulphuric acid p.89
Cells and batteries p.150

REACTIONS

Alkalis and bases

When YOU BRUSH YOUR TEETH with toothpaste, you are using a
base to get rid of the acids that form in your mouth when foods break
. down. Bases are substances that can cancel out acidity. They are said
to neutralize acids. Alkalis are bases that can dissolve in water.

» Bases and alkalis are all around us - in oven cleaners, polish,

■ft baking powder, indigestion tablets, common plants, saliva, and
■ chalk. Like acids, some alkalis are very dangerous and can cause
burns if splashed onto the skin. All alkalis dissolve in water to
V form hydroxide ions (OH'). These ions react with the hydrogen
ions (H + ) in acids to cancel out acidity. The number of
Br hydroxide ions an alkali can make in water is a measure of its
r strength. This is measured on the pH scale.

ALKALI FROM ASHES

The word alkali is Arabic and means the “ashes of a
plant.” Alkalis used to be made by burning wood and
other plants - sodium carbonate from sea plants

and potassium carbonate from land plants. jHH

Alkalis are now made by electrolysis.

SOAP

Alkalis feel soapy when rubbed between the
fingers. This is because they react with the oils
in our skin and start to dissolve them. Soap is
made by boiling animal fats or vegetable oils
with the strong alkali sodium hydroxide.

This is a type of
alkaline battery you
might find in a watch
or a calculator.

ALKALI ON METAL
When a solution of
sodium hydroxide is
poured onto some pieces
of magnesium metal,
there is a tremendous
fizzing. This is hydrogen
gas that has formed
during the reaction.
Magnesium hydroxide is
left in the flask. This is
the active ingredient in
milk of magnesia, which
people take to cure
indigestion - it works by
neutralizing excess acid
in the stomach.

ALKALI CONDUCTORS
Since alkalis break up in water
\ to form ions, alkalis are
good conductors of
electricity. In an
—alkaline battery,

IIII 3 ] the strong alkali

potassium hydroxide
BB9r is used to conduct
— ~ electricity between
two electrodes.

Negative zinc
electrode\

Potassium
hydroxide
electrolyte -

Positive -
mercury
oxide
electrode

WARNING SYMBOL
v Concentrated solutions of
alkali are corrosive and
can cause severe burns.
Wy? Because of this, the
A/ containers in which they are
/ stored and transported always
carry a hazard warning sign.

ALKALIS IN SPACE
Astronauts in the Apollo space missions
used the alkali lithium hydroxide to
neutralize the dangerous levels of
carbon dioxide gas they were breathing
out. This type of neutralization is also
used to remove carbon dioxide from
air-conditioned buildings.

Sodium hydroxide mixed
with magnesium pieces

Calcium carbonate

Seashells, coral, chalk, limestone, and marble are all made of the base
calcium carbonate. It is a very important and useful compound in the
chemical industry for making fertilizer, glass, cement, and steel. By
heating calcium carbonate, calcium oxide (quicklime)
is made. Just by adding water, this can be
made into calcium hydroxide (slaked
|jj|^ lime), which is used to neutralize
^ acid in water supplies. Slaked
lime can be mixed with sand
^^mrirsr f j f1 1 and water to make mortar.

Limestone¬
processing plant

?/)

REACTIONS

The more hydroxide ions an alkali contains, the stronger it is,
and the higher its pH. All alkalis have a pH greater than 7.

Alkali half of the pH scale

Alkalis can be used to
clean brass.

Negative -
hydroxide ion

STRONG ALKALIS

Some alkalis, such as sodium hydroxide and potassium hydroxide,
are called strong alkalis. When they dissolve in water, all their
molecules dissociate (split up) into ions. This means they contain
many hydroxide ions, and so have a high pH. Oven cleaners, for
example, contain the strong, corrosive alkali sodium hydroxide.

This reacts with the burned, fatty deposits that form on the oven
walls during cooking.

A bee sting is very painful
because it contains an acid.

This can be neutralized by

In a strong alkali, many
hydroxide ions have split off
from the positive ions.

Positive ion

In a weak alkali, only
a few hydroxide ions
have split off from

the positive ions. . , _

H x 7 WEAK ALKALIS

Some alkalis, such as
ammonium hydroxide and
baking soda (sodium hydrogen carbonate), are weak alkalis. In solution,
only a few molecules dissociate into ions. They therefore contain only a few
hydroxide ions, which gives them a low pH. Brass cleaner is a weak alkaline
solution. It works by breaking down the oxide layer that forms on the
surface of the brass when brass is left exposed to the air.

LIMING FIELDS AND LAKES

Acid rain increases the acidity of the lakes and soils on which it
falls. This takes out essential nutrients from the soil. To fix this,
farmers spread powdered lime (calcium hydroxide) on
their fields. The lime is a base that
neutralizes the acidity. Lime can also
be added to lakes to reduce acidity.

Adding lime to lakes and fields can
relieve the damage caused
by acid rain, but it does
not stop the cause of
the pollution.

Farmer
liming field

Baking

soda

Sulfuric

acid

A wasp sting is very painful,
because it contains an alkali,

This can be neutralized by ftif!
adding an acid.

FIRE EXTINGUISHER
Some fire extinguishers work by
using the neutralization
reaction between an acid and a
base. They contained sulfuric
acid and baking powder, which
mixed when the extinguisher
was turned upside down. This
produced water aiid carbon
dioxide gas. The pressure of
this gas forced a foam of
liquid and carbon dioxide
bubbles out of the nozzle.

The fizzy reaction
between the acid and
the alkali forces out a
foam, which can be
used to put out fires.

Neutralization

Every time a base meets an acid, neutralization
occurs, and water and a compound called a salt are
produced. This reaction can be used to treat some
animal and plant stings. If you are stung by a wasp's
basic sting, you can neutralize it with an acid such
as lemon juice or vinegar. If you are stung by a bee
or an ant, you can neutralize the acid sting with an
alkali such as baking soda. Nettles also give acidic
stings, which can be treated by rubbing with a leaf
of a dock plant, which contains an alkali.

ALKALI IN THE PLAGUE
Seventeenth-century London, England, was an unhealthy
place to live in and was continually ravaged by plague -
the plague of 1665 killed 80,000 people. The bodies
were buried in mass graves covered with a
strong alkali, lime, to speed up the rate of
decomposition (rotting).

Find out more

Bonding p.28
Solutions p.60
Acids p.68

Measuring acidity p.72
Salts p.73

Alkali industry p.94

REACTIONS

Measuring acidity

Beetroot Radish Pear Red cabbage

The inner circle is the
universal indicator colour 3
scale. It is pink in strong acid
(pH 1) and blue in strong
alkali (pH 14). The outer
circles show how the colour
of the juices of red cabbage,
pear, radish, and beetroot
change as the pH changes.

HAVE YOU NOTICED how the colour of tea changes
slightly when you add a slice of lemon? The tea is acting
as an indicator, showing that the lemon has increased
the acidity. Some coloured chemicals are used in the
same way to show whether a solution is acid or
alkaline. A measure of the acidity or alkalinity
of a solution is called pH, short for “power of
hydrogen”. This is a scale that runs from 1 to
14. It is based on the number of hydrogen ions
a solution contains. A pH of 1 shows the
solution contains many hydrogen ions and is
a strong acid. A pH of 14 indicates that the
solution contains few hydrogen ions and is a
strong alkali. Neutral solutions have a pH of 7.

Indicators

There are many
different indicators

Contact lens solutions and
injections have to be buffered
so the pH of
your body
fluids is
not altered.

BUFFERS

Sometimes, we don’t
want the pH of a solution
to change. In the body,
for example, most
reactions will only take
place within a narrow
range of pH. A
change of just 0.5
in the pH of your
blood could kill you.

To prevent this from happening,
the body produces substances
(called buffers) that neutralize
any changes in acidity or
alkalinity and keep the pH of
the blood constant. For the same
reason, intravenous injections
have to be carefully buffered.

IABORATORY
INDICATORS
Scientists often use special
laboratory indicators to
help find when just
enough acid has been
added to neutralize all
the alkali in a reaction.

Two examples are
methyl orange and
phenolphthalein. These
change colour at a precise pH.

Hydrangeas
grown in acid soil
produce blue flowers.

NATURAL INDICATORS
Some plants are natural indicators.
The colour of hydrangeas depends
on whether the soil is acid or
alkaline. Litmus is an indicator
obtained from a plant called a
lichen. Litmus paper is made by
soaking paper in litmus solution. It
turns red in acid and blue in alkali.

Alkalis turn litmus Acids turn litmus

Methyl orange is orange
between pH 4 and 8.

pH METER
A very accurate measure of the pH
of a solution can be found by
using a pH meter. It uses an
electrode to measure the
concentration of hydrogen
ions in solution and
displays the pH of the
solution, either digitally or
by a needle on a scale.

SOIL ACIDITY

Gardeners often have to worry
about the pH of their soil. Some
plants will only grow in a certain
pH range. Soils in chalk and
limestone regions are usually
alkaline (pH 7 to 7.5). Soils in
sandstone, clay, moorland and
peat areas are usually acidic (pH
6.5 to 7). Heather prefers to grow
on acidic soils, and that is why it
often covers open moorland.

Phenolphthalein is
colourless below
pH 8.5.

Methyl orange is
red below pH 3.

Methyl orange is
yellow above pH 8.

Hydrangeas grown in
alkali soil produce red
flowers.

Phenolphthalein is
deep pink above
pH 9.5.

that can tell us the
acidity or alkalinity of a
solution. A very useful
indicator is a mixture of dyes known
as universal indicator. This gives a range of
colour changes from red for pH 1 (very strong
acid) to blue for pH 14 (very strong alkali).
The dyes obtained from fruits and vegetables,
such as pears, onions, and red cabbage, can
also be used as indicators. They change colour
as the pH changes. The juice of a red
cabbage, for example, turns from red in
strong acid, through to pink, purple,
blue, and green in strong alkali.

Find out more

Bonding p.28
Hydrogen p.47
Reversible reactions p.54
Solutions p.60
Chemical analysis p.62
Acids p.68

Alkalis and bases p.70

REACTIONS

Tarnished copper

The copper is
cleaned by a lemon.
In doing so, a salt is
made that dissolves
in the lemon juice.

COPPER SALT

Copper easily reacts with oxygen from
the air to form a thin coating of copper
oxide. Copper that has tarnished in this
way can be cleaned with lemon juice.
The acid in the lemon juice (citric acid)
reacts with the copper oxide (a base) to
form a salt (copper citrate) and water.
This salt will dissolve in water, leaving
the copper clean and shiny.

Common salt is
made up of
sodium ions (Na + )
and chloride
ions (CT).

Salts

ions

All salts are made up of ions. It is
because of these ions that salts are
able to dissolve in water, and their
solutions will conduct electricity.
The strong ionic bond explains why
salts usually have such high melting
and boiling points.

HAVE YOU WONDERED why the sea is salty?
Salts are naturally occurring compounds that
are often soluble in water. Rivers dissolve salts
from the earth and carry them down to the
sea. The salt we put on food is just one type of
salt. But there are many others. In fact, salts
are very common and useful chemicals.

Plaster of Paris, gunpowder, chalk, paint
pigments, garden insecticide, and fertilizers
are all examples of salts. They are compounds
of a metal and a non-metal joined together
by an ionic bond. A salt is made whenever an
acid reacts with a metal or a base, and they
usually form beautiful crystals.

BODY SA1.TS

The next time you sweat, see how salty
the sweat tastes. Every time you sweat,
you lose salt from your body. Because
salt is vital to the healthy running of
the body, this can lead to dehydration
and collapse. This is why doctors
advise people to take salt tablets when
they visit hot countries. This replaces
the salt that is lost in sweat.

Dilute

sulphuric acid

Tiny blue crystals of the salt, copper
sulphate, start to appear once the
solution is heated.

Nerve

When the acid mixes with
the black copper oxide, a
blue solution of copper
sulphate is made.

Making a salt

Every time an acid
and a base are mixed,
a salt is made. If black
copper oxide (a base) is mixed with dilute
sulphuric acid and heated, a blue solution is
created. The base has neutralized the acid and
a dissolved salt, copper sulphate, has been
formed. The water from this solution can be
boiled away, until the blue crystals of copper
sulphate slowly start to appear.

NERVES

Messages in your body are
carried as electrical signals
along nerve fibres. When there is a
gap between two fibres, the signal is
carried across by potassium and
sodium ions in the cell fluid. These
vital ions come f rom the salts you eat.

Blue copper

sulphate

crystals

SALT FAMILIES

In a salt, the metal (copper) comes
from the base (copper oxide) and the
non-metal part (sulphate) comes from
the acid (sulphuric acid). Each acid
therefore has its own family of salts.
Sulphuric acid makes sulphates, citric
acid makes citrates, and so on. Each
base also forms a family of salts.
Copper oxide, for example, always
makes copper salts.

The heat
from the
bunsen
burner drives
off the water from
the solution, leaving
the salt behind.

NATURAL SALTS
Many ores and minerals
are made of salts. These
include limestone
(calcium carbonate),
gypsum (calcium
sulphate), and fluorite
(calcium fluoride). If
they grow in the right
conditions, all salts will
form beautiful cry stals.

Bunsen

burner

Salts often
make beautiful
crystals.

Fluorite

crystal

Find out more

Bonding p.28
Cr\stals P.30
Compounds and
mixtures p.58
Solutions p.60
Acids p.68

KALIS AND BASES P.

REACTIONS

DISCOVERIES

1754 Scottish doctor Joseph Black
finds carbon dioxide in air.

1772 Scottish physician Daniel
Rutherford finds nitrogen in air.

1774-79 Joseph Priestley (English)
and Antoine Lavoisier (French)
find oxygen in air.

1892-98 British scientists Sir
William Ramsay and Lord Rayleigh
find air contains inert gases.

Air contains
many different
colorless
gases.

Chemistry of air

Air quality

Human activities have
caused changes in the
composition of the
air. For example,
silver tarnishes
because sulfur in
the air reacts with it
to form a layer of silver
sulphide. It wasn’t necessary to clean silver until around
1600, when the levels of sulfur in the air began to rise. The
biggest changes have occurred since the Industrial
Revolution in the 19th century, when people began to burn
carbon fuels on a large scale. Carbon dioxide makes up a
larger part of air today than it ever did before. We must
control the pollution of our air to protect life on Earth.

ESSENTIAL AIR
It is easy to forget that we are
surrounded by air. But without it,
many of the things that we take for
granted could not happen. For
example, if you took a car to the
Moon, it would not work because
there is no air there. This is why
astronauts have to use an electric
car when they explore the Moon.

Nitrogen boils at -305°F
(-196°C). It is used to make
fertilizers, and nitric acid.

The INVISIBLE BUT VITAL AIR surrounds us all the time. It
is a mixture of different gases, mainly nitrogen and oxygen.
We are constantly changing the composition of the air
around us - just by breathing, we are reducing the
amount of oxygen it contains. The air in the
atmosphere is like a protective shield. It filters out the
Sun’s harmful ultraviolet rays but allows the visible
and infrared rays, on which we depend for light and
heat, to pass through. The air in the atmosphere also
acts like an insulating blanket, preventing extremes of
temperature. Without it, the Earth would be like the
Moon - boiling hot by day, and freezing cold at night.

Nitrogen makes up
78% of the air.

makes up
21% of the air.

Argon makes up
0.9% of the air.

Gasoline-
driven cars
cannot
be used on the
moon.
Astronauts must
use electric cars.

Carbon dioxide makes
up 0.03% of the air.

amounts of
other gases make up the
remaining 0.07% of the air.

LIFE-GIVING AIR
All life depends on
air f or its survival.

We use the oxygen
in air to convert food
into energy, and we
breathe out carbon
dioxide. Plants use
a reaction called
photosynthesis to convert the carbon
dioxide from the air into foods, such
as sugars, which they need to grow.

FRACTIONAL DISTILLATION OF AIR
Air contains some very useful gases. They can be
separated by a process called fractional distillation.
Air is made into a liquid by being cooled to a very
low temperature. When it is left to warm up, the
gases boil off the liquid at different times since they
have different boiling points. The gases can
therefore be collected separately.

Oxygen boils at -361 °F
(-183°C). It is used for
scuba tanks.

Liquid

Argc
boils ,
-367 1
(-186°C
It make
an unreactii

On Earth, a car
continually takes in air.
The oxygen in the air is
needed to bum gasoline
- the energy released
the reaction drives the

Find out more

Nitrogen p.42
Oxygen p.44
Noble gases p.48
Behavior of gases p.51
Compounds and
mixtures P.58
Oxidation and

REDUCTION P.64

Industrial pollution p.112
Atmosphere p.248

REACTIONS

Chemistry of water

DON’T BE FOOLED BY WATER. What appears to be just a

colorless, odorless, tasteless liquid is actually a chemical whose

reactions with other substances are vital to life. Water is a a

compound of hydrogen and oxygen. Its chemical jpj

formula H 2 0 shows that each molecule of water

contains two atoms of hydrogen and one atom of

oxygen. Water is not only all around us, in rain,

clouds, and the seas; it is inside us as well. Water rg|

carries nutrients to your cells, and waste

products from your body. Water is very good at i

dissolving substances. Because of this, it is

hardly ever found in its pure form. The water. , \

from a tap, for example, has been in contact

Thin people may contain as
much as 75% water; fat people
i may contain only 55% water.

There
are more

molecules of * ^ h 1

water in just one drop
than all the millions of
stars we can see in the sky.

At room temperature, pure

water is a colorless liquid, i?:- :
It boils at 212°F (10CPC), %
freezes at 32°F (CPC), and
Df has a neutral pH of 7.

A tomato
contains
95% water.

Water covers over
70% of the surface
of the Earth.

Hard water

Hard

Certain dissolved chemicals make water “hard,
water does not easily form a lather with soap. Instead,
a white precipitate, scum, is formed. There are two
types of hardness in water. Calcium and magnesium
hydrogen carbonates cause temporary hardness,
l' which can be removed by boiling. This makes a solid
t (calcium carbonate) - the scale (hard build-up) found
' in kettles. Permanent hardness is caused by calcium
and magnesium sulfates. These can be removed by
passing the water through a water softener, which swaps
the magnesium and calcium ions for sodium ions.

WATER EVERYWHERE
Water is the most common chemical
compound, and covers over 70 per cent of the
Earth’s surface. On average, the human body is
about 65 per cent water. Some foods are almost
totally water. A ripe tomato, for example, is 95
per cent water. In all these places, the water
carries out important chemical functions.

WATER IN AIR
On a humid day, the air j
contains a lot of water J
vapor. Humidity is a M
measure of the amount
of water in the air. Dry
air, such as that in a ]
desert, contains very ]
little water vapor. 1

Adding water to white
copper sulfate crystals
turns them blue.

SOLID WATER

Unlike most other substances, water expands when it
freezes. When water molecules join up to form ice, a
hydrogen atom from one molecule joins to an oxygen
atom from another. This creates a hexagon
(six-sided) shape, with an empty space in
the middle. This explains both why ice is | ‘ \
less dense than water and why snowflakes
are based on this hexagonal shape.

Desert plants "
require less «**
water than <
most other plants.

WATER OF CRYSTALLIZATION
Many compounds contain water
molecules trapped in their crystals.
This is the water of crystallization.
It can be driven off by heating. If
blue copper sulf ate crystals are
heated, they lose their water of
crystallization and turn white.
Adding water to these white
crystals turns them blue again.
Because only water can produce
this color change, the process is
used as a chemical test for water.

Find out more

Hydrogen

atom

Changes of state p.20
Bonding p.28
Cr\stals p.30
Solutions p.60
Water industry p.83
Humidity p.252
Snow p.266

Oxygen

atom

Water

molecule

•\VV\V

REACTIONS

Chemistry of the body

Your body is a mobile chemical factory that processes

raw materials, such as food, water, and oxygen. After being fed in,
these raw materials go through a series of complicated chemical
reactions, known as metabolism. This produces the energy the
body needs to function. One series of reactions breaks down large
molecules of food into smaller ones, such as glucose, that can pass
into the bloodstream. This process is called digestion. The blood
transports the glucose to the liver, where it is stored as the body’s
fuel. The cells release the energy in this fuel by a reaction called
respiration. Waste products are taken for disposal to the end of the
body’s factory line.

Making glucose

In the intestine, the food is bombarded by a
mix of chemicals called bile. This is
piped in from the liver, via
the gall bladder. It
contains bile salts
which help to break
down fats. Enzymes to
complete the digestion
of food come from the
pancreas and the
intestine wall. Glucose,
/ one of the products of

/ all these reactions, is

I transported to

the liver.

Gallbladder

SALIVA
The first site of
chemical attack on the
food that we eat is our mouth.
Here, saliva pours out of the
salivary glands and onto the food,
which is being ripped apart by our
teeth. The saliva is a watery mix
that contains an enzyme called
amylase. This enzyme starts to
break down the starch in food.
Since amylase will only work in
alkaline conditions, saliva is very
slightly alkaline.

While the stomach enzymes are
working, the contractions of the
stomach wall work like a liquidizer,
pounding the food into a fluid
called chyme. ^

STOMACH

Once the food has reached the stomach, it is
swirled around with gastric juices, which
have poured from the gastric glands. Gastric
juices contain a strong acid called
hydrochloric acid and several enzymes. The
acid kills germs in the food and activates an
enzyme called protease, which
breaks down proteins. —

Hydrochloric acid is made
in the gastric glands by a
chemical reaction
involving carbon dioxide,
water, and salt.

The bile contains
bicarbonate of soda
(sodium hydrogen
carbonate), which
neutralizes the acid
from the stomach.

Oesophagus

Heart

CATABOLISM —

Some chemical reactions in the body
produce energy. Respiration, for
example, releases energy by breaking ^

down glucose into smaller molecules. This
energy is not produced as a result of breaking
the glucose bonds but is released when
stronger bonds are formed in the smaller
molecules. Energy-releasing reactions are
called catabolic reactions, and the
itself is called catabolism.

Intestine

The chyme from
the stomach is
piped into the
small intestine.

Stomach is
behind liver

process

Liver

ANABOLISM

Chemical reactions in the body that involve
building up structures are known as anabolic. They
differ from catabolic reactions as they use up
energy, rather than release it. They get this energy
from all the catabolic reactions in the body.
Making blood proteins involves building large,
complex molecules from simple ones. It uses a
great deal of energy and is an anabolic reaction.

The process itself is called anabolism.

Intestine

REACTIONS

ENZYMES

Many chemical reactions in the
body are speeded up by special
catalysts called enzymes. Each
enzyme helps with one
particular reaction. They are
cleverly able to distinguish
between molecules that are very
similar, so they will not speed
up the wrong reaction. Enzymes
are remarkably efficient and fast¬
working catalysts. Without them,
our body reactions would be so slow
that we would certainly die.

BODY ELEMENTS

Your body is made up of many dif ferent
chemical elements. Oxygen, carbon,
and hydrogen are found in the fats,
proteins, and carbohydrates that make
up most of the body tissues. Nitrogen is
found in proteins, and bones contain
calcium. Trace elements in the body
include iron, sodium, potassium,
copper, zinc, magnesium, phosphorus,
iodine, chlorine, silicon, and sulphur.
These elements, although present in
only minute amounts, are essential for
keeping the body healthy.

LIVER

The liver is the body’s chemical
powerhouse. It produces a green
liquid, bile, that aids digestion,
and it keeps a store of glucose,
vitamins, and minerals. Poisons
from drugs and alcohol are also
removed from the blood by the
liver. The reactions that occur in
the liver are mostly exothermic,
which means they give out heat.
This heat is spread around the body
by the blood to keep us warm.

BLOOD

Red blood cells contain haemoglobin, a
compound of protein and iron, which
combines with oxygen in the lungs
and transports it to all the body’s cells.
When the oxygen has been released for
cell respiration, haemoglobin loses its
bright red colour and becomes
purplish. It then combines with the
waste carbon dioxide produced by the
cells and deposits it in the lungs so that
it can be breathed out.

Respiration

Oxygen

65 %

Other elements
1 %

Phosphorus
1 %

Calcium

2 %

Nitrogen

3 %

Carbon

18 %

Hydrogen

10%

Glucose from the
liver is given to the
blood.

Amazingly,
the kidneys
can filter all the
body’s blood in only five
minutes. The dissolved waste,
urine, flows into the bladder.

The energy contained in food is converted into energy we
can use by a chemical reaction called respiration. This
reaction is carried out in every single cell of our body and
in nearly all living cells in the world. There are two kinds
of respiration: aerobic and anaerobic. Aerobic respiration
requires oxygen. It releases a great deal of energy.

Liver

Oxygen + glucoses carbon dioxide + water + ENERGY

A burning nut gives out heat and light energy. This reaction is very
similar to aerobic respiration. In both cases, food combines with
oxygen to give energy. But inside your body, the energy is not suddenly
released as a flame, it is released more gradually in chemical form.

ANAEROBIC RESPIRATION
If you are running fast in a race,
your muscles are using up oxygen
faster than your lungs can take it in.
The cells start to use anaerobic
respiration to give you extra energy.
This reaction does not require
oxygen but produces less energy
than aerobic respiration does.

Glucose —> lactic acid + energy

Lactic acid causes muscle ache and cramp.
This is why athletes take deep breaths at
the end of a race, to replace oxygen
supplies and to get rid of the lactic acid.

The liver stores
vitamins, regulates
the amount of
glucose in the
blood, purifies the
blood, and gets rid
of excess protein.

Solid
waste is
excreted.

The

kidneys are in

charge of the

body’s cleaning and

waste disposal. Millions of small

filters, called nephrons, remove poisons

and waste substances from the blood.

Blood ft

is busy

travelling to every ^
cell of your body. On its
journey, it picks up
glucose from the liver and
oxygen from the lungs.
These two chemicals are
needed by every cell for a
reaction called respiration.
This releases all the a
energy our body ^0.
needs.

Find out more

Catalysts p.56
Chemistry of food p.78
Digestion p.345
Cellular respiration p.346
Blood p.348

Internal environment p.350

REACTIONS

Carbon

atom

Hydrogen

This is a molecule
from the herb
oregano. It has 10
carbon atoms, 14
hydrogen atoms, and
1 oxygen atom.

Oxygen

atom

CHEMICAL PIZZA
A pizza is really just
a plate of chemicals,
and most of them are
good for you. The
hundreds of different
chemicals present
have very complicated
formulas. Just look
at the complicated
chemical above,
which gives the
herb oregano
its flavor.

Fat is not
present

There are more chemicals in the food you eat than

you would ever find in a laboratory. Many of the chemicals
contained in food are vital to life. Groups of chemicals called
proteins, carbohydrates, fiber, fats, vitamins, minerals, and
water are all needed for a healthy diet. Other
chemicals are responsible for the flavor, while
still more may give the food color. Oil from an
orange peel contains around 50 different
chemical compounds. Whenever food is
cooked, reactions occur that change these
chemicals. In fact, cooking and chemistry
have a lot in common. Many of the
processes used, such as heating, mixing,
and filtering, are very similar.

PROTEIN TEST

Food scientists test a food for proteins by crushing up a
sample with water. If dilute sodium hydroxide, followed
by a few drops of copper sulfate solution, are added, the
color will change from pale blue to pale purple if
protein is present in the food.

FAT TEST
Fats are large molecules of
carbon, hydrogen, and oxygen,
found in foods such as cheese,
peanuts, and butter. A food sample
can be tested for fat by shaking it in
ethanol (a type of alcohol). Any fats
in the food will dissolve, to give a clear
solution. This is then poured into a
tube of water. Because fats are
insoluble in water, tiny droplets of
fat will cloud the water, if fats are
present in the food.

Protein is not
present

The protein chains in a
raw egg are neat
spiraled chains.

Proteins

Life-building chemicals
called proteins are found in foods
such as eggs, meat, and nuts. They
are made up of carbon, nitrogen,
sulfur, oxygen, and hydrogen atoms.

Some protein molecules are joined together in
long, spiraled chains. As you cook an egg, the
protein molecules first unravel (called
denaturation) and then tangle up together,
forming a solid mesh. This is why the protein
white of an egg becomes solid when cooked.

As the egg
is heated,
the protein
chains start
to unravel.

Protein is
present

When the chains are
unraveled, they become
tangled with each other
and form a solid mesh.

Chemistry of food

up an onion make
you cry? Onions contain a number of
unusual sulfur compounds. When the
onion is cut, these react with oxygen in
the air, to form strong-smelling
chemicals that cause your eyes to water.
Scientists have recently discovered that
some of the sulfur compounds may be
useful for treating asthma.

MINERALS

The tiny amounts of inorganic substances we need
in our diet are known as minerals. Water dissolves
these minerals, containing the elements calcium,
iron, potassium, and magnesium, out of the soil.
They are then taken up through the roots of the
plants growing in the soil. By eating these plants,
we also eat the minerals they contain.

REACTIONS

VITAMINS

The vitamins are a mixed assortment of chemicals
that are only needed by the body in small amounts.
They are found in many foods, such as citrus fruits
(vitamin C), green vegetables (vitamins A and K),
carrots (vitamin A), wholewheat bread (vitamin B)
and oily fish (vitamin D).

Vitamin C is
not present

LEMON PRESERVATIVE
Freshly cut fruits, such as apples
and bananas, soon become
brown when they are exposed to
the air. This is a reaction between
chemicals in the fruit and oxygen,
speeded up by an enzyme in the fruit.
As enzymes are very sensitive to changes
in acidity, the browning reaction is
slowed down by adding an acid, such as
lemon juice, to the freshly cut fruit.

PRESERVING FOOD
Fresh foods, such as fish, soon go bad if they are left in
the open air, because harmful microbes start to grow on
them and inside them. But food can be preserved by
killing the microbes or by slowing down their growth.
There are a number of common methods for doing
this. Freezing, salting, smoking, and pickling all slow
down, or even stop, the microbes from multiplying.
Heating or passing radiation through the food are the
only ways to kill all the microbes.

Vitamin C is
present

v v

VITAMIN C TEST

There is a blue dye, called DCPIP, which vitamin C
can turn colorless. If this change happens when a
sample of food (crushed in water) is added to the dye,
it proves that the food contains vitamin C.

SUGARS

The sweetness of jams and cakes is due to a group of chemicals called
sugars. These are compounds of carbon, hydrogen, and oxygen.
One of the simplest sugars is glucose. Its chemical formula is
^6^12^6- Other simple sugars include lactose, which is
found in milk, and fructose, which is found in fruits.

Sugars are not confined to the
kitchen any more. Industrial
chemists have started to
convert sugars into industrial
chemicals, which are used to
make paints and detergents.

CARAMELIZING SUGAR
When sugar is heated the
sugar molecules start to
break down, giving off
water. If the heating is
continued the sugar
caramelizes, becoming
dark brown and sticky.
Caramel is used as a
coloring for vinegar,
gravies, and other

^ , , foodstuffs.

Caramelized

sugar

Fish are

smoked by holding them
over a wood fire. The heat from the fire and the chemicals in
the smoke slow down the rate at which microbes grow.
Smoking also adds flavor and changes the texture of food.

STARCH TEST

Starch can be detected by crushing up a
food sample with water and adding a few
drops of iodine solution. If the food
turns a blue-black color, it shows
that the food contains starch.

Starch is not
present

Pasta,
potatoes,
and rice all
contain starch.

Starch granules in
water, magnified
60 times

starch

SUGAR TEST

A food can be tested for sugar by
crushing it up with water and
adding a special chemical called
Benedict’s solution. If an orange-
brown precipitate forms when
this mixture is heated, it shows
that sugar is in the food.

Sugary

foods

FOOD POISONS

Some foods naturally contain tiny
amounts of poisons, which in very
large doses can make us ill. Bananas
contain a chemical that can produce
hallucinations. Green potatoes
contain a poison, solanine,
which causes stomach ache.

Cheeses can contain tyramine,
a chemical related to the body
hormone adrenaline. This
affects our pulse rate and
can cause nightmares.

Starch is
present

Starch

Starchy foods, such as bread,
potatoes, rice, and pasta, are
made up of sugar molecules
joined together in long chains.
Starch and sugar are sometimes
called carbohydrates. The starch
in flour is used to thicken sauces
like gravy. When starch granules
are heated in water, some water gets
inside them and forces the individual
molecules inside the granules apart. This
causes the granules to swell up
until they burst, leaking the
starch molecules into the
surrounding liquid, and
thickening the sauce.

Find out more

Organic chemistry p.41
Chemical anal\sis p.62
Chemistry of the body p.76
Fermentation p.80
Food industry p.92
Nutrition p.342
Digestion p.345

REACTIONS

Magnified
view of yeast
cells

Fermentation

Yeasts are tiny living organisms
that are only visible through a
microscope. Yeasts grow
on the skins of fruits,
such as grapes and
apples, by feeding
on sugars. Each
yeast cell divides
rapidly as it feeds.

Yeast converts
the sugar into
alcohol, which
is left in the
flask, and
carbon
dioxide gas.

Airtight

stopper

FOR THOUSANDS OF YEARS, fermentation has been
used to make bread, beer, and wine. Today, it is used to
make foods such as bread and yoghurt, alcoholic drinks such
as wine, drugs such as penicillin, and chemicals such as methanol
and citric acid. Fermentation is a chemical process. Tiny organisms
called microbes grow by converting the sugars in foods, such as
fruits and grain, into alcohol and carbon dioxide. Microbes can
live almost anywhere. It is likely that fermentation was discovered
by accident when fruits or grain were stored in containers. One
safe and commonly used microbe is yeast. Not all microbes are safe
to eat - many are harmful and poisonous.

MAKING BREAD
One of the ingredients of bread is yeast.
After the dough has been kneaded, it is
put in a warm place. The yeast respires
with oxygen by feeding on the sugars
and breaking them down into carbon
dioxide and water. These gases cause
the dough to rise. As you bake the
dough, the yeast is killed, and the
gases expand to give the bread a
spongy texture. If dough without yeast
is used, it will not rise. The bread it
makes is called unleavened bread.

The gas given off
travels through this
tube to the limewater.

Bubbles of
gas forming

The clear
limewater
turns cloudy
after mixing
with the gas.
This proves
the gas is
carbon
dioxide.

When water is
mixed with the
flour and the
dough is
kneaded, some
of the proteins
in the flour
combine to
form a network
of molecules
that is strong
and elastic.

Yeast mixed
with warm
water and
sugar

FIRST FERMENTATION
The Ancient Egyptians were the first to
make leavened bread 5,000 years ago.
They used to keep a store of sour
fermented dough (called sourdough)
that was added to each mix to make
the bread rise. Sourdough was
probably discovered when yeast
spores were blown onto dough that
had been mixed and put to one
side before baking.

Yeast

If a mixture of yeast, sugar, and warm water is left to stand,
bubbles of gas appear as the yeast ferments. If this gas is
bubbled through limewater (a solution of calcium
hydroxide in water), it turns the limewater cloudy. This
result proves that the gas is carbon dioxide - the cloudiness
in the limewater is the insoluble compound calcium
carbonate suspended in the water. The yeast is
respiring without oxygen. This

means it feeds on the sugar,
converting it to carbon
dioxide and alcohol,
which is left in the flask.

Lactobacillus
bulgaricus bacteria,
magnified

YOGHURT

Yoghurt is made by adding certain bacteria
(lactobacilli) to milk and allowing this to ferment
without oxygen. The bacteria multiply and cause the
milk to thicken. They reduce the sugar content by
converting the milk sugar, lactose, into lactic acid.
This is why natural yoghurt tastes sour.

ALCOHOL
Microbes will normally
produce carbon dioxide and
water by respiration (as in
bread-making). However, if the
microbes do not have a good
supply of air, they make carbon
dioxide and alcohol. This is why
alcoholic drinks are made by
carrying out the fermentation
in sealed containers. When the
solution contains around 14
per cent alcohol, the microbes
become poisoned, and
fermentation stops. This is why
alcoholic drinks with more than
14 per cent alcohol cannot be
made just by fermentation.

BLUE CHEESES
A special type of penicillin
mould is added to blue
cheese to give it its colour and
taste. As the cheese matures,
small holes are made in it
with stainless steel needles to
ensure that the mould has
enough oxygen to grow.

Find out more

Chemistry of the body p.76
Chemistry of food p.78
Single-celled

ORGANISMS P.314
Fungi p.315

Asexual reproduction p.366

MATERIALS

Imagine what life would be like if

you wore concrete shoes and rode
bicycles made of glass. These are just two
of the many materials we use in our daily
lives - but not for walking or cycling!
Most of the materials around us have
been changed from their natural state.
The original materials come from
substances in the ground, in water, or
even in the air. Chemical processes
change these raw materials into
materials with special properties that
we can use. For example, the
materials in our clothes are made
from fibres that are stretchy, soft, and
strong. This makes our clothes
comfortable and hard-wearing.

Materials for tennis

All the materials used in a game of tennis are
perfectly suited to their functions. Rackets are strong
because they need to stop balls that are travelling
very fast. Balls are made from materials that do not
tear when they collide with the racket or the court.
Tennis shoes and the court surface are both made of
tough materials to withstand the wear and tear
caused by players running all over the court.

are made
from rubber,
nylon, and
natural fibres.

before baking, people could make bowls,
cups, and urns to hold food and drink.

They called this material terracotta, which
means baked earth. This was one of the
first manufactured materials.

TERRACOTTA

About 7,000 years ago, people found that
if they heated clay it changed into a hard,
brittle substance. By shaping the clay

CLOTH STEAMS AHEAD
Since 8000 b.c. people have been
spinning natural fibres to make
threads, and weaving or knitting
them together to make cloth. In
the late 18th century, Europeans
invented machines that could spin
and weave using steam power.

AGE OF PLASTICS

In the 1850s, Alexander Parkes, an English
chemist, made the first plastic material. Today,
plastics are made from the chemicals in oil.
They are used to make toys, as well as many
household products, such as bins and chairs.

EXTRACTING IRON
The Hittites of Turkey
discovered how to extract iron
3,500 years ago. The secret was
to heat rock containing iron
with burning charcoal. This
made the metal soft enough to
hammer into weapons and tools.

A sports cap is made of
cotton for keeping cool.

Sunglasses made from
chemicals in oil are light
and safe to wear.

Sports socks are
! e of natural fibres
to keep feet cool.

Wood is a tough
and hard natural
material made
from trees.

Sports clothes are
made from strong,
comfortable
materials, such as
polyester, cotton,
and nylon.

Sports shoes
are made from leather or canvas,
with rubber soles for flexibility.

Racket frame is made of
plastic containing graphite,
synthetic leather-
cushioned grips, and
synthetic strings.

FROM IRON TO STEEL
Early metalworkers knew that
carbon could make iron
harder. In 1742, an English
inventor called Benjamin
Huntsman found away to
control the amount of carbon,
to produce the first true steel.
Steel is now used to make a
range of products from
needles to car bodies.

Paper consists of natural
fibres made from trees.

MATERIALS

Chemical industry

People in nearby
towns are employed to
work in the plant.

SMALL-SCALE MODEL
Before building an
industrial plant, a small
scale model is built in a
laboratory. Chemicals
are passed through
glass apparatus to make
each stage of the
process easy to see and
check. When the
scientists are sure the
chemical reactions and
equipment work safely,
this model is scaled up.

SCALING UP
When the small-scale
model is running well,
and ways have been
investigated to make the
material cheaply, the
equipment and
processes are scaled up
to make a full-size plant.

IN THE PIPELINE
Color-coded pipes transport
cooling water, steam, liquid, and
chemical gases around industrial
plants.

Raw
materials
must be
stored near
the plant.

Materials MADE IN THE CHEMICAL INDUSTRY are all around you;
some are inside you, too. These materials range from the paint on cars to
the food you eat. Each material is made in a factory called an industrial
plant. Raw materials, such as minerals, oil, water, coal, and gas, enter the
industrial plant, where chemical reactions take place. These reactions
change the raw materials into useful materials like steel, iron, and gasoline.

The useful materials are then transported to be used by
people all over the world. Industrial plants are very
expensive to build and run. They are one of the
largest industries in the world, and their aim
is to make materials at prices people
can afford.

Energy provides
the power to run

This industrial plant is conveniently
located for raw materials, workers,
and transport.

Some waste materials are
recycled to make other products.

It is vital to

have roads and rivers
nearby to transport
materials away quickly
and efficiently.

Cows eat pellets
made from
harmless waste
food materials.

Boat to transport
materials

The site

An industrial plant
needs raw materials,
energy, and water. These
must be close to the plant for it
to work efficiendy. Materials
made in the plant must be
cheaply transported away, and
waste materials must be carefully
disposed of. Some wastes are
sold to make into other useful
materials. This is recycling.
Waste materials that cannot be
sold are made as harmless as
possible before being released
into the environment.

KEEPING SAFE
Chemical reactions can produce
poisonous fumes, start fires, and
cause explosions. Industrial workers
are protected from such hazards by
safety equipment and warning
systems in the plant. Special
protective clothing is provided in
case of such emergencies.

Find out more

Che

Indu<

:mical reactions

^ATER INDUSTRY P.£
STRIAL POLLUTION
JERGY SOURCES P.L

Fact finder p.406

p.52

p.112

MATERIALS

Water industry

A PERSON CAN LIVE for about six days without water, but most
industries would stop working immediately without it. Industry needs
large amounts of water to make almost all the materials we use. Every
day, the world’s industries use on average four times as much water as
people use in their homes. Rain is the main source of all this water, but
before we use it, it must be cleaned. When rain hits the ground, it
rushes into streams and rivers, or sinks into rock beneath the ground.
On its journey, the water picks up small particles of rock, bacteria from
the soil, and dissolved chemicals from almost everything it flows over.

DESALINATION

Lemonade Shower Steel Car

WATERFACTS
To make a car requires 8,000
gallons (30,000 liters) of water.
To make 1 ton of steel requires
1,125 gallons (4,500 liters) of
water, but a shower will use
only 9 gallons (35 liters). One
liter of lemonade uses 2
gallons (8 liters) of water.

Water is trapped behind a dam
in a reservoir .»

In the chemical filter, aluminum sulfate
(alum) and calcium hydroxide (lime) are
added. These form a sticky substance,
aluminum hydroxide, which traps any
suspended particles in the water.

The water travels through
beds of sand and gravel,
where dirt particles
are trapped\

In places where there is little rain, such as
the Middle East, people obtain water
from the sea. The seawater is heated, at
low pressure. Only the water evaporates
and is condensed in collecting trays. The
salt is left as a concentrated solution.

Not all

industries need
very pure water.

Some, such as power
stations, can use the impure
water straight from rivers or the sea.

HOW INDUSTRY USES WATER
Industry uses large amounts of
water. The water cools furnaces
where chemical reactions release
heat, provides the heat to start a
chemical reaction, or generates
steam to drive a pump or electrical
generator. Used as a solvent, water
dissolves many substances, making
the diluted solution easier to
handle. Finally, water cleans
materials, equipment, and the
workplace.

Water

storage

towers

Any bacteria that
survive the filters are
killed in the contact tank
by chlorine gas which is
bubbled through the water
for about an hour.

To stop bacteria
reinfecting the water,
low doses of chlorine
are left in it when it is
sent to our homes.

Manufacturing
a car involves a
surprising
amount of water.

Purifying water

Rivers, lakes, and
underground
wells are nature’s stores of water, but
artificial reservoirs allow us to
store large amounts of water near
factories and homes. As the water leaves
the reservoir, it passes through a screen
to remove objects such as leaves and
twigs. Filters made from chemicals, sand,
and gravel remove smaller particles that
could scour (wear away) the inside of
water pipes, damage industrial
equipment, or make drinking water
cloudy. Bacteria or viruses, which may
cause disease and death, are dealt with
by bubbling toxic gases, such as
chlorine or ozone, through the water.

Find out more

Changes of state p.20
Solutions p.60
Separating mixtures p.61
Chemistry of water p.75
Chemical industry p.82
Factfinder p.406

MATERIALS

CAST IRON

The dome of the Capitol, in Washington D.C.,

Iron and steel

WITHOUT IRON AND STEEL, what would we use for making
cars, supporting tall buildings, or producing machines to make
nearly every product there is? Iron is the cheapest and most
important metal we use. Iron is extracted from a rocky material
called iron ore, and most iron is then made into steel. Like many
elements, iron is too reactive to exist on its own in the ground.
Instead, it combines with other elements, especially oxygen, in
ores. The chemical process for extracting a metal from its ore is
called smelting. Iron ore is heated with limestone and coke,
which is mostly made up of carbon. Coke and limestone remove
the unwanted parts of the iron ore to leave almost pure iron,
which still contains some carbon. Steel is made by removing
more carbon and adding other metals.

contains 4,000 tonnes of cast iron. The different
parts were made by bei ng cast in a mould.

Waste gases
are cleaned and
used to heat the
hot-air blast y

Safety

valve

The blast furnace

Iron is extracted from iron ore in blast furnaces.
The biggest are 60 m (200 ft) high, produce
10,000 tonnes of iron a day, and work non-stop for
10 years. The furnace gets its name from the blast
of hot air that heats up the raw materials. These
are iron ore, limestone, and coke (a form of
carbon). As carbon is more reactive than iron, it
grabs the oxygen from the iron ore, leaving iron
metal behind.

Raw materials —-
enter through two
bell valves. The
valves prevent
hot gases
escaping. A

HENRY M ^1

BESSEMER

Steel is the ^(3

most usef ul Wm y

form of iron,

but removing aBp

the carbon jff- .-i

f rom the iron

used to be an

expensive process.

In 1856, a British inventor, Henry
Bessemer (1815-1898), devised a
cheap way of removing most of the
carbon. Air was blown through the
molten metal in a furnace called a
converter. The oxygen in the air
removed the carbon.

Furnace
lined with
l heat-
\ resistant
A bricks

Limestone

Bustle pipe around
furnace delivers a
blast of hot air.

This gives the
furnace its name.

Coke, made
by heating
coal without
air present

INSIDE THE BI AST FURNACE
The chemical reactions begin
when hot air is blasted into the
furnace. As the coke burns, the carbon
in it gets enough energy to react with
oxygen from the air to form first
carbon dioxide and then carbon
monoxide. The carbon monoxide takes
oxygen atoms from the iron oxide to
leave carbon dioxide and iron metal.
Temperatures inside the furnace reach
1,900°C (3,500°F), melting the iron
which sinks to the bottom.

Ladle for
carrying
molten iron

Outlet for
molten slag

IMPURITIES

Iron from a blast furnace is
90-95 per cent pure. The main
impurity is carbon, absorbed
from the coke in the blast
furnace. Carbon makes the iroi
hard but not very strong. Most
iron is converted'til to steel, a
form ofifcm that contains less
Mian 1.7 per cent of carbon.

IRON IN CLOSE-UP
Cast iron can be
made in a number
of different forms.

In the form shown
here, magnified 200
times, tiny spheres
of graphite (blue)
make the cast iron
hard but ductile.

SLAG

Limestone is
included in the
f urnace because it \
mixes and combines
with sand, clay, and
stones in the ore. They
form a waste material,
called slag, which floats i
top of the molten metal.

Outlet for
molten iron.

MATERIALS

CONTINUOUS

CASTING

Steel scissors
contains about
1 per cent
carbon.

Molten steel is poured between water-cooled
rollers that shape and cool the steel until it
solidifies. The rollers form the metal into
standard shapes, such as slabs or bars,
known as billets.

Molten
steel in
reservoir

Water-cooled

rollers

A steel anchor chain
contains about
0.1 per cent carbon.

Stainless steel in the laboratory

DRAWING A rod becomes wire if squeezed
through a series of small holes.

ROLLING

A series of rollers shape a billet into
rods, tubes, girders, or rails.

Steel billet

A metal block presses the
steel with a force of up -
to 10,000 tonnes. Jm

FORGING

Rotor shaft of a
turbine engine

More than one steel

There are carbon steels and alloy
steels. Low-carbon steels are
tough yet easy to shape. High-
carbon steels are hard and
brittle, but can be given sharp
cutting edges. Alloy steels
contain a range of metals,
each giving the steel a special
property. Chromium, nickel,
and steel make stainless steel,
which is hard-wearing and
does not rust. /

Steel slab

Steel is poured into a mould,
and solidifies in the shape of
the mould as it cools.

Train wheels

Molten steel CASTING

Molten iron poured
into furnace

Shaping

steel

Steel can be
shaped in a variety
of ways. Rolling stretches and
squeezes ingots of steel into
sheets, tubes, or strips. In
drawing, rolled steel is pulled
through a hole to make a wire.
In casting, it is left to cool in a
mould. Forged steel is made
by squeezing hot steel.

Oxygen is blown onto
the molten metal.

The oxygen combines with
carbon in the iron to make
carbon monoxide. This
reaction releases heat,
and the iron stays
molten. ,

Scrap steel forms up to
a quarter of the molten
metal used. _

Lime removes impurities such as
phosphorus. The lime reacts with
the impurities to form a slag that
floats on the steel.

AFTER THE FURNACE
The ladles of molten steel are
poured into moulds to make
ingots, or a reservoir that sen es a
continuous casting process. Most
steel is continuously cast because it
is cheaper and better quality. •
These blocks of steel, called billets,
can then be shaped by rolling,
forging, or casting.

Ingots of steel

When the process is
\ complete, the furnace tilts to

pour the steel into a ladle. Slag is
removed by turning the furnace upside down.

Basic oxygen furnace

Most iron is converted into steel in a
basic oxygen furnace. A mixture of
iron and steel scrap is poured into
the furnace, and a jet of oxygen is
blown over it. Oxygen combines with
the carbon in the iron, carrying it
away as carbon monoxide. It takes a
basic oxygen furnace just 40 minutes
to produce 350 tonnes of steel.

Find out more

Transition metals p.36
Carbon p.40
Oxidation and
reduction p.64
React ivity series p.66
Coal products p.96
Sedimentary rocks p.223
Factfinder p.406

STEEL IN CLOSE-UP ■
This picture shows a low-
carbon steel, containing 1H
0.87 per cent carbon. The it
structure of steel is varied "
with different amounts of
carbon and by the way it cools.

MATERIALS

COPPER

YOU MAY NOT BE ABLE TO SEE IT, but
copper is all around you. The walls and ceilings
of almost every room in your home contain
copper wire leading to light fixtures and
electric outlets. These wires carry the electricity
that provides light and power in our
homes. In its natural form, copper
occurs in the ground as copper ore, a
mineral. But this ore contains only
F*F“ 0.5-1 percent of the metal. The rest is
rock. The world produces 9.6 million
tons of copper a year. This means that
more than a billion tons of ore has to be
removed from the ground and the

Outlet for 0 ,

copper pure copper extracted.

Extracting copper

Most copper is extracted from a
compound of iron, sulfur, and copper
called sulfide ore. Hot air is blown into a
furnace to separate the copper from the
| iron and sulfur. The iron and sulfur react
I with the oxygen to form iron oxide and
I sulfur dioxide, leaving molten copper
1^ metal. This copper, known as blister
I copper, is about 98 percent pure. A
I process called electrolysis is needed to
separate the remaining impurities.

^ Pure copper collects at cathode A

W - the negative electrode. J

Chalcopyrite is a
sulfide ore - it
contains copper,
combined with
iron and sulfur.

Sulfide

ore

LEACHING

In some ores, the copper is combined
with oxygen. In a process called
leaching, sulfuric acid is sprayed over
these copper oxide ores, dissolving
the copper but not the rock. The
copper and sulfuric acid form a
solution of copper sulfate, which is
purified by electrolysis.

Outlet for

sulfur

dioxide

Outlet for I
iron-silicate
slag (waste)

bPIL CARRIE EVERSON

■QBk Ores contain a mixture of

valuable metallic substances
and worthless rock. An
American schoolteacher,
Carrie Everson, invented a
way of separating the two
in 1886. She ground up ore
and mixed it with oil and
acid. This produced a froth
in which the metallic
substances floated, while the

^ rocky materials sank.

Carrie Everson

Silica is added
and reacts
with iron oxide
to make iron-
silicate slag.

The molten copper is cast
into flat slabs. Each slab
of blister copper is about
3 ft (1 m) across and
weighs 900 lb (400 kg).

Electric coils in motor

ELECTROLYSIS
A slab of blister copper can be
transformed into pure copper
by electrolysis. The slab is
suspended in a solution of
copper sulfate and sulfuric
acid, where it acts as a positive
electrode (anode). When
electricity is passed through
the solution, the copper in the
anode is dissolved. The pure
copper collects at the negative
electrode (cathode),
and the impurities
j^H^^^*£Lfall below.

Solution of '
copper sulfate and
sulfuric acid

copper

Copper ions move
toward the cathode

Blister copper acts'
as anode - the
positive electrode.

Impurities
collect as
slime

Micrograph
of copper

USES OF COPPER
Copper is a good conductor of heat
and electricity. We use it to make
cooking utensils and all sorts of pipes
for carrying hot water, both in homes
and in industry. We also use it to make
different kinds of electrical devices,

«l such as

m ■ electric coils in
I motors.

I Copper does
■ S not rust easily,
I so it lasts a very
1 long time.

Atoms of copper stack 1
together in a regular
way as the metal forms
to make crystals. The
way the crystals interlock
allows the metal to be easily
pushed or pulled into shape.

Find out more

COPPER BY-PRODUCTS
Gold, silver, and platinum can be
found in their pure state in the
Earth’s crust, so they do not have to be
extracted from ores. However, useful
amounts are found in the slimes that
form during the electrolysis of copper.

Transition metals p.36
Reactivity series p.66
Electrolysis p.67
Alloys p.88
Sulfuric acid p.89
Fact finder p.406

Platinum

MATERIALS

The Emperor of
France, Napoleon III
(1808-73), used
aluminum plates to
impress his most
important guests. Today
we use aluminum foil to
wrap food because it is
so inexpensive.

YOU’VE PROBABLY SEEN aluminum in the
form of soft drink cans or thin sheets of foil.. It
is the most common metal on Earth. It occurs
naturally in many different kinds of rock. But
most of the aluminum we use is extracted from
an ore called bauxite. Because aluminum easily
combines with other elements, a great deal of
energy is needed to separate it into its metallic
(pure) form. Chemists discovered a cheap way
of extracting aluminum in 1886. Before this,
the metal was much more expensive than silver
and gold.

CYCLESUPPORT
Aluminum is easy to
work and shape. As a
tubular frame, it
provides a very
lightweight support for
the racing cyclist.

The major aluminum
ore, bauxite, is formed
over long periods by
the weathering of rocks
containing aluminum
silicates (aluminum,
silicon, and oxygen). ^

Huge wheel
extracts
bauxite ore
from the
Earth’s crust.

Each cell (used for
electrolysis) is up to
30 ft (9 m) long by 13
ft (4 m) wide. Carbon
anodes hang in the
molten cryolite.

Extracting aluminum

Aluminum is extracted from bauxite by the
Bayer process and by electrolysis. In the
Bayer process, bauxite is mixed with caustic
soda and heated. This produces sugar like
crystals of pure aluminum oxide. These are
dissolved in molten sodium aluminum
fluoride, called cryolite. Electrolysis is then
used to split up the aluminum and oxygen.

Electric current passes
through the liquid,
driving the oxygen
1 '■■■■■Miiiiii from the
\ aluminum

\ oxide to the

\ anodes.

The bauxite
ore is
crushed
into pieces.

Sodium hydroxide is
added to bauxite and
pumped into a large tank
called a digester.

Molten
aluminum
collects at the
carbon
cathode,
which lines
the bottom
and sides of
the cell.

Heat and high pressure help
sodium hydroxide digest (break
down) bauxite. Aluminum oxide
from the ore dissolves, forming a
solution of sodium aluminate. A filter
removes the insoluble impurities.

Digester

Crystals of
aluminum oxide
form as the
solution cools,
leaving sodium
hydroxide.

Heat drives water
from crystals, to
leave a fine powder

Aluminum is
collected and
used to make
many products.
It can also be
easily recycled.

COINCIDENTAL CHEMISTS

In 1886, two chemists independently discovered

how to extract aluminum using electricity.

Their discovery reduced the price of aluminum
to a fraction of the price of silver in four years.
The two chemists were Charles Martin Hall
(1863-1914), a student at Oberlin College in
Ohio, and P. L. T. Heroult (1863-1914), a
young chemist working in France. By

coincidence,
they were not
only the same
age when they
made their
discovery, but
also died within
eight months
of each other.

P.L.T. Heroult

Find out more

Poor metals p.38
Reactivity series p.66
Electrol\sis p.67
Allo\s p.88
Factfinder p.406

using aluminum

When the surface of aluminum
reacts with oxygen in the air, a thick coating of aluminum
oxide forms. This seals the metal from the air and stops it
corroding. Aluminum is also durable, light, and a good
conductor of electricity. So we use it to make parts for
planes, cars, and trucks, and to make electric cables.

MATERIALS

Alloys

If YOU HAD BEEN A SOLDIER in Ancient Greece you would
have had to stop in battle to straighten your bronze sword. But
bronze was a great improvement on copper, which bends even
more easily. Most pure metals are weak and soft. But two soft
metals mixed together make a harder metal called an alloy.
Bronze is an alloy of copper and tin. By changing the amounts
and combinations of the metals, the properties of an alloy can
be altered. Most alloys consist of two or more metals, but some
contain a non-metal, such as carbon. The most widely used alloy
of this type is steel.

Aluminium mixed with
magnesium and
copper provides a
lightweight body that is
W strong enough to stand
r up to high-speed winds and
the impact of landing.

THE FIRST ALLOY

About 6,000 years ago, people discovered that
copper could be made harder if mixed with tin.
This alloy is called bronze. It was so widely used
for many years that this period of time became
known as the Bronze Age.

HIGH TEMPERATURES
A drill bit cuts its way
through hard material,
spinning thousands of
times a minute. A
tungsten carbide alloy,
with a melting point of
over 2,900°C (5,250°F),
provides the hardness
and strength to do this.

In a jet engine, metal discs
hold the turbine blades in
place. Discs are made from
a superalloy of 11 elements
including nickel and titanium.

Alloys in aircraft

Jet aircraft need lightweight alloys for their bodies to
make take off easier and to keep fuel consumption
down. Their engines need special alloys designed to
withstand very high temperatures. Rapidly spinning
turbine blades at the front of the engine suck in air
at temperatures of up to 600°C (1,100°F).

LOW TEMPERATURES
Solder, an alloy of tin and lead, is
perfect for joining metal parts
together. It has a lower melting
point than either of its pure
metals, so it does not damage any
of the parts. It creates a bridge
between the two metal parts.

MAKING ALLOYS

Most alloys are made by melting metals
and mixing them together. Gare must
be taken to make sure that one metal
does not boil before the other melts.
When making brass, for example, solid
zinc is dropped into molten copper. If
the zinc were heated to the same
temperature as the copper, it would
boil away into a vapour.

Find out more

DENTAL ALLOY
You may have an alloy in your
teeth. Dentists use amalgam - the
alloy of mercury, silver, tin, zinc,
and copper - to fill cavities. It
forms a solid that can be shaped
like putty to match the contours of
the teeth before it hardens.

Bonding p.28
Alkali metals p.34
Transition metals p.36
Poor metals p.38
Reactivity series p.66
Fact finder p.406

Metals in an alloy dissolve in each other.
Their atoms mix freely and lock together
to make strong crystals when they cool.

MATERIALS

Sulphuric acid

Sulphur (a
" solid element)
is the key raw
material in
sulphuric acid.
But water and air
are also needed.

What do fertilizers, paints, explosives, and

detergents have in common? They are all made with
sulphuric acid. In fact, many of the items we use every day
would not exist without it. Sulphuric acid does not occur
naturally; it has to be manufactured. The chemical industry
produces about 150 million tonnes of it each year.
Fortunately, sulphuric acid is cheap to make because the
waste heat from one stage of the process can be used to
provide heat for the next stage.

The steam from a
coiled pipe melts the
sulphur, which is
then sprayed into a
furnace.

Heat exchanger

Dry air is blasted into
the furnace. Oxygen
in the air combines
with sulphur to make
sulphur dioxide gas.

In the converter,
more oxygen is
added to the sulphur
dioxide to make
sulphur trioxide.

JEAN ANTOINE CHAPTAL
In the 18th century, factories
used sulphuric acid for making
plaster, dyes, and buttons. The
French chemist Jean Antoine
Chaptal (1756-1832) saw the
need to make sulphuric acid
on a large scale for these and
other rapidly growing
industries. In the 1780s, he set
up the first commercial factory
for making sulphuric acid at
Montpellier, France.

Converter

In the heat x.
exchanger, the
sulphur dioxide
passes over a pipe of
water, heating the water
as it cools. This heat is used
to melt the sulphur and drive the
fans that blow air into the furnace.

Absorber

Sulphur trioxide passes
through a spray of
sulphuric acid which
absorbs the sulphur
trioxide. This forms a
concentrated fuming
_- liquid called oleum.

SULPHUR TRIOXIDE
Without a catalyst, sulphur
dioxide and oxygen are slow
to react. Pellets of
vanadium pentoxide act
as a catalyst to speed
things up. They provide
a huge surface for the
molecules to settle on.

This draws the molecules
close together, so that
they start reacting.

Oxygen

Sulphur dioxide

Sulphur trioxide
forms at the
surface

Sulphur
trioxide could
be added
directly to
water to
^ produce
sulphuric
acid.
But the
reaction
would be too
violent.

p Making acid

There are two stages in
making sulphuric acid. First,
air and sulphur are heated to make
sulphur dioxide. In the second stage
air and sulphur dioxide are mixed
to produce sulphur trioxide, and
this gas is dissolved in sulphuric acid
to give oleum, a super concentrated
form of sulphuric acid.

Vanadium

pentoxide

The oleum is diluted with
water to make sulphuric acid of
_ the right strength.

Manufacturing

chemicals

Other uses

MAKING RAYON
A bath of sulphuric
acid is essential for
making rayon, a
synthetic fibre. Strands
of syrup, made from
wood pulp, pass
through 10,000 holes
in this head. The acid
in the bath hardens
the strands into 10,000
solid threads of rayon.

USING SULPHURIC ACID
15% j Industrially, sulphuric acid is a very
useful chemical because it reacts
readily with other materials,
13% removing metals, oxygen, water, and

other unwanted substances. Apart
I from manufacturing other chemicals,
sulphuric acid is also used in car
j&iWteW batteries, oil refining, and

Detergents and soaps f or cleaning metals.

Dyes and
pigments -

Find out more

Sulphur p.45
Catalysts p.56
Oxidation

AND REDUCTION P.64

Acids p.68
Ammonia p.90

Fertilizers

Plastics and fibres

MATERIALS

RAW MATERIALS
Hydrogen and
nitrogen are the raw
materials for
ammonia. Hydrogen
is made by reacting
methane in natural
gas with steam.
Nitrogen is extracted
from the air.

Ammonia

Nitrogen

Fritz Haber

Haber’s apparatus for making ammonia

Making ammonia

Today, ammonia is still
made in plants that have
Bosch’s basic design. The
process is very complicated.
It involves several stages,
including purifying the
nitrogen and hydrogen.

The most important stage,
though, is converting
nitrogen and hydrogen to
ammonia. Bosch did 6,500
experiments to find that the
best catalyst for speeding up
the reaction was iron.

Fertilizers

If YOU’VE EVER HAD a whiff of ammonia, you know how strong the smell
is. In the 19th century, a weakened form of ammonia (a compound of
nitrogen and hydrogen) was used in smelling salts to revive people who had
fainted. A pure form of ammonia would have been dangerous. Today,
ammonia is an important raw material for many chemical processes and
products - especially fertilizer. Much of the 140 million tons of ammonia

produced each year is used to make fertilizers. These
Hydrogen j L give pi an ts the nitrogen they need to grow. In fact,

it was the shortage of nitrogen fertilizers that led
to the development of a process for
manufacturing ammonia on a large scale. Modern
ammonia plants make hundreds of tons of this
every day.

Carl Bosch

FRITZ HABER AND CARL BOSCH
In 1908, the German chemist Fritz Haber (1868-
1934) used this apparatus (left) to produce
ammonia. Making nitrogen and hydrogen react
together was not easy, but Haber calculated how
to make the reaction work. Five years later, Carl
Bosch (1874-1940) had scaled the experimental
apparatus up to industrial size. Bosch, a German
industrial chemist, had to design large pieces of
equipment that would endure the high pressures
and temperatures needed to make ammonia.

Pure

hydrogen

Less than one-third of the hydrogen
and nitrogen is converted to
ammonia. The uncombined gases are
i recycled until they form ammonia too.

USING AMMONIA
Ammonia has many uses
apart from fertilizers. Large
quantities of ammonia are
converted into nitric acid.
The acid is used to make
nylon, explosives, varnishes,
lacquers, and rocket
propellants. Urea, made
from ammonia and carbon
dioxide, is used as a food
supplement for
farm animals and
in plastics.

Nylon

Modern ammonia plants are huge. This
equipment removes carbon dioxide from
hydrogen - just one stage in preparing
one of the raw materials from methane.

The hot gases
are pushed
through a 65 ft
(20 m) tall
catalyst
chamber.

Cooling

chamber

The
gases
are squeezed
by a pressure 250 times
greater than the air
around you and heated
to 850TF (450PC).

Other uses

When

the hot gases
touch the catalyst
(pellets of iron), they are drawn
together and react to form ammonia.

ACID TO FERTILIZER
Farmers use ammonium salts
as a fertilizer. These are
made by mixing
ammonia gas with hot
nitric acid and then
spraying the solution
into the top of a tower.
The droplets fall into a
rising current of cold
air and form pellets.

The gases are cooled
until ammonia liquefies
and can be drained off.

Find out more

Bonding p.28
Nitrogen p.42
Hydrogen p.47
Catalysis p.56
Fact finder p.406

MATERIALS

Chemistry in farming

CHEMICAL FOOD
In addition to their natural
food, farm animals eat
pellets of chemicals. These
contain extra nitrogen to
help build strength and
speed up growth.

Every DAY THE HUMAN POPULATION increases by about 200,000
people. Soon there will be more than six billion mouths to feed. In order
to provide enough food, farmers will need the help of the chemical
industry. This industry produces fertilizers that contain minerals for
plants. Without minerals, plant growth is poor, and food production is low.
Some chemicals control the ripening of fruit, so it doesn’t go bad before
you eat it. Chemical food supplements for farm animals help them grow
faster and avoid disease. But many people are
concerned about the amount of chemicals we
use to produce food. Too much fertilizer
leads to water pollution, and some
pesticides kill harmless plants and animals
and are dangerous to people’s health.

INSECT KILLERS
Insecticides kill in three different
ways.If an insect touches contact
insecticides, eats stomach
poisons, or breathes in
fumigants (poison gas), it
will die.

ORGANIC
FARMING

The crops
and livestock
on an organic
farm do not
receive any
synthetic chemicals
in fertilizers and food Seaweed
supplements. Organic farmers
treat the soil with manure, to
provide minerals for the crops.
Every year, they grow a different
crop in each field, so that all the
plants can benefit from the range
of minerals in the manure. This
also disrupts the lives of pests and
keeps their numbers low.

Organic farm animals get
supplements from natural
chemicals found in seaweed.

Fungus can
destroy a
whole crop
of wheat.

Weeds deprive
other plants of
space and food.

Insects
eat their
way through
crops of corn.

FUNGUS KILLERS
Fungicides are
organic chemicals
that may contain
zinc or manganese.
Farmers spray them
on crops or put them
in the soil. This stops
the fungus from
spreading and destroying
the whole crop.

WEEDKILLERS

Herbicides kill weeds in a variety of ways.
Some interfere with photosynthesis and
stop the weed from making food. Others
work by poisoning the growing cells at the
tips of the roots and shoots.

Pest killers

Any living thing that disrupts the
growth of crops or livestock is a pest.

It may be a weed competing with crop
plants for space, water, and minerals.
It could also be a fungus sending out
its feeding threads to destroy plant
tissue, or an insect eating its way
through leaves, fruits, and roots.
Farmers reduce the number of pests
by using pesticides - chemicals
designed to stop one or more life-
giving reactions in a pest’s body.

CHEMICALS TO GROW CROPS
Fertilizers provide the range of minerals that
plants need. Each mineral helps the plant to grow
in a different way. To test the effects of a fertilizer,
farmers grow two groups of plants and give
fertilizer to one group. Then they compare the two
groups at the end of the growing period.

Find out more

Alkali metals p.34
Nitrogen p.42
Phosphorus p.43
Alkalis and Bases p.70
Factfinder p.406

MATERIALS

FOOD INDUSTRY

FREEZE THEN DRY
Astronauts rely on freeze-dried
food. In the freeze-drying process,
the food is frozen, and then the
water is removed. You can keep
freeze-dried food at room
temperatures because bacteria
cannot live without water.

IN THE CAN

Walk into any supermarket and
you’ll see lots of canned food.
Canning is the most popular way of
preserving food. Fresh foods are
first boiled for a short time, to
destroy their enzymes, and then put
in cans and heated to kill bacteria.
Finally, the cans are sealed to
prevent air bringing oxygen and
bacteria to the food again.

QUICK FREEZING
Bacteria cannot feed and breed if the
food is frozen. In fluidized freezing,
small items of food, such as peas, pass
over a blast of cold air (-34°C or -29°F)
on a conveyor belt. The air makes the
peas rise and move freely over one
another like particles in a fluid. The
peas freeze in minutes.

Most of the food in your last meal was probably harvested on a farm
many weeks ago, but it still tasted good. The food industry processes much
of our food with chemicals so that it remains edible and safe, and looks

attractive, for a long time. Without these chemicals, microbes (bacteria and
fungi) would get to your food before you had a chance to eat it. Microbes
produce compounds that taste and look unpleasant,
and may be toxic. Food processing began thousands
of years ago to help people keep food
through the lean winter months. Today,
food processing allows food from other
parts of the world to be transported

to OUr local shops SO that We After cows are

can enioy a great variety ' , milked, a tanker

J ] o / transports their milk to

of things to eat all f ^ the dairy.

through the year.

The milk is heated
to pasteurize it

The solid lumps are
called curds. They are cut
up to help the watery part
of the milk (the whey) drain
away. The whey is made
into food for farm animals.

Special bacteria are added to
the milk. They feed on
lactose (milk sugar), making
lactic acid in the process. The
acid thickens the milk and
makes it turn sour.

PASTEURIZATION
Boiling kills bacteria, but also
destroys nutrients. In the
pasteurization process, liquids such
as milk are heated to 70°C (160°F)
for 15 seconds and then cooled
quickly. The flavour is preserved
while the bacteria are destroyed.

The milk is warmed and
rennet, which comes
from calves’ stomachs,
is added. Rennet
contains an enzyme
called rennin that
makes part of the
milk thicken into
solid lumps.

From milk to cheese

Milk is a watery solution of protein, sugar,
vitamins, and minerals, with fat droplets to
make the milk white. But it also contains
bacteria that feed, breed, and make the milk
sour in a few days. Our ancestors discovered
that they could preserve the nutrients in milk
by turning it into cheese. Today, there are
many varieties of cheese, but most of them
share the basic stages of production.

Salt is added to the curds, and they are pressed
to remove any remaining whey. The curds are
shaped into moulds and stored on cool shelves
and left to ripen into cheese.

MATERIALS

HELPFUL MICROBES

Grape juice in these vats is being turned into wine
by the action of millions of tiny yeast cells. This
fungus has been used f or thousands of years in making
alcoholic drinks and bread. Today, the use of microbes
to make materials for us is called biotechnology.
Microbes can make useful materials from unlikely
substances. Some microbes can turn methanol, made
f rom natural gas and waste products f rom the paper¬
making industry, into food for f arm animals.

Additives

It does not take long to
collect the foods shown here
for a snack. Snacks should
only be eaten occasionally
because of the high level of
fats and sugar they contain.
They also contain chemicals
called additives. The food
industry uses additives to
stop food from going bad
before we eat it. Additives
also keep food looking
attractive and tasting good.
There are hundreds of
different additives, some
natural and some synthetic. .

EMULSIFIERS
Normally f at and water
quickly separate. But
emulsifiers, such as lecithin
from egg yolk, keep
them in place fjjfL

in yoghurt,
chocolate, and
ice cream.

Tiny yeast cells

ANTIOXIDANTS
Fats react with oxygen to make
acids, which turn the food
rotten. Antioxidants prevent
this from happening. For
example, a synthetic chemical,
butylated hydroxy-toluene
(BHT), will stop the fat in corn
chips going rotten.

In biscuits, bases
such as sodium and
ammonium hydrogen
carbonate improve
flavour and prevent
changes in acidity
and colour.

PRESERVATIVES
Salts and sugar can poison and
kill bacteria and fungi. This is
why sodium nitrite is added to
salami and hot dogs, and
potassium sorbate to chilli dip.
These preservatives make your
food last longer.

In bread rolls, a
natural chemical
such as vitamin C
(ascorbic acid)
stops oxygen
reacting with the
fat in the bread.

The conveyor belt
moves food at the
correct speed to
receive the permitted
dose of radiation.

In the food
chamber, food
passes through the
electron beam at
two different
heights and
distances to make
sure that it is
completely
irradiated.

COLOURINGS

Natural pigments may break up, leaving the food
looking pale and unappetising. A stronger natural
colouring, such as beta carotene from carrots,
keeps your orange juice looking orange.

Irradiation

Food irradiation uses
radiation or high energy
electron beams to preserve
food. The radiation or
electrons pass into the food,
killing harmful microbes.

But in fruits and vegetables,
irradiation slows ripening
and stops further growth.

The technique also alters the
molecules of the food itself,
and can destroy vitamins and
other nutrients. Because of this,
and because of fears about levels
of radioactivity in
treated food,
irradiation

remains a
controversial
technique.

Sweets have synthetic
colourings from dyes,
which tempt us to eat them.

Electron gun releases high-
energy electrons.

Scan horn keeps the electron
beam in a small area of the
processing plant.

The scan

chamber

FLAVOURINGS
Drinks such as cola contain
natural flavouring chemicals.
But if the chemicals break
up, flavour is lost. So
synthetic chemicals, which
are stronger tasting and less
likely to break up, copy the
natural chemicals.

FOOD PROCESSING

4000 B.c. Salt and chemicals in
smoke are used to preserve food.

3000 B.c. Yeast is used to make
alcoholic drinks by
fermentation.

a.d. 200 Bacteria is used to
make yoghurt by fermentation.

1804 Nicolas-Frangois Appert
(1752-1841) discovers a way of
preserving food in sealed
containers. Canning industry is
developed from his discovery.

1860s Louis Pasteur (1822-95)
invents a way of killing harmful
microbes in wine and beer.

1920s Clarence Birdseye (1886-
1956) develops a method for
quick-freezing food.

Find out more

Radioactivity p.26
Oxidation and
reduction P.64
Chemistry of food p.78
Fermentation p.80
Fact finder p.406

MATERIALS

Alkali industry

Chloride ions form
chlorine gas, which
leaves the solution.

A partition stops

Sodium hydroxide is made bypassing electricity
through brine in these cells.

Sodium hydroxide

Salt dissolved in water
consists of four different ions
(particles): sodium,
chloride, hydrogen, and
hydroxide. During
electrolysis, a current C
of electricity draws

The SALT WE SPRINKLE on our food can also be used to make
the soap that we rub on our skin. Salt, also known as sodium
chloride, can be made into two different alkalis: sodium hydroxide
and sodium carbonate. These are used to make many products. Of
all the alkalis produced in the industry, these two are the most
important. Each year, chemical plants throughout the world
produce about 35 million tons of each alkali. Sodium hydroxide is
made by passing a current of electricity through a salt solution
called brine. This also produces chlorine, which is why the alkali

A industry is also known as

Hydrogen ions collect at the [he chlor-alkali industry.

/ * cathode and escape from 1

the neii as hvdmnen nas Sodium carbonate can be

made from brine
and carbon dioxide.

the negative ions (chloride
and hydroxide) to the
anode, and the positive ions
(sodium and hydrogen) to
the cathode. When separated
from the chloride, sodium
reacts with the water, to form
sodium hydroxide.

Ammonia
and

Waste gas

The strength of the
sodium hydroxide
can be increased by
evaporating some of
the water contained
in the solution.

Solution
of sodium
hydroxide
in water

Miscellaneous

Carbon dioxide
rises up through
tower and

cniorme from
reaching the
sodium hydroxide
and reacting with it.

Cathode

Making

Artificial

fibers

Carbon dioxide

Carbon dioxide
released from
crystals is recycled.

USING SODIUIM
CARBONATE
You’ve probably seen
this alkali in the form
of bath crystals or
detergent. But it is also
used in making a wide
range of products from
ceramics and textiles to
photographs and
leather goods.

Float glass
and other
glass ,

and recycled.

from the solution.

Sodium carbonate

Brine will absorb carbon dioxide to
form sodium carbonate. In the Solvay
process, carbon dioxide is dissolved in
brine saturated with ammonia. This
produces crystals of sodium hydrogen
carbonate and ammonium hydroxide
solution. The crystals are then heated
to form sodium carbonate.

Steam pipes heat the
crystals to drive off carbon
dioxide and
water.

Glass

containers

50%

0 %

15%

25%

Paper

making

Soaps

Neutralization

Detergents

Chemicals

USING SODIUM HYDROXIDE
Alkalis are well known for
neutralizing acids. But in industry,
sodium hydroxide has many other
uses, including making bleaches,
drugs, dyes, and oil products, as
well as processing foods, metals,
and rubber.

TRONA ORE
In parts of the United
States and Africa,
trona ore provides a
source of sodium
carbonate. Trona ore
is sodium hydrogen
carbonate, easily
refined without using
the Solvay process.

Find out more

Bonding p.28
Alkali metals p.34
Halogens p.46
Electrolysis p.67
Alkalis and Bases p.70
Factfinder p.406

MATERIALS

Soaps and detergents

IMAGINE HOW DIRTY you would be without soap. Water can
dissolve many dirty substances, but it cannot dissolve grease.
Certain salts of sodium, known as soap, can break up the
grease so that the water can wash it away. Soap is made by
reacting sodium hydroxide with animal and vegetable fats /
or oils. Some kinds of water, however, contain chemicals
that react with the soap to form a white insoluble
powder, called scum. Detergents copy the action of

scum

Floor cleaner

Shampoo

Dishwashing

liquid

f / Water
/ molecules
/ attract water-
loving heads.

Grease and
detergent
molecules
are lifted into the
water and
washed away.

soap without making scum. To make detergents
chemicals from crude oil are reacted with
sulfuric acid. j

Detergent molecules _ S OjJ IN

in water /(T h D Jfl uj lit

Water-loving -A-O M- ~ 7 WKHwSttisOv

heads (-P V *0

Grease-loving ~ ^^SajjySp^fe^ )? Ju I ’ '

DIFFERENT CLEANERS
Cleaners help us in many different
ways. Soap coats your skin in
grease-removing molecules.
Shampoo has extra chemicals that
make the lather stay in place on
your hair while attacking the
grease. Floor cleaner has chemicals
called builders that clear away
gritty dirt, while dishwashing liquid
has other chemicals to clear away
greasy scraps of food.

Lumps of grease
on a dirty surface

The tails of the J9
detergent

molecules surround the

grease and then sink into it. The water-

loving heads stay on the outside.

Water

Sodium

hydroxide

At high
| pressure, fats
jjl and oils react
Brf with hot water
^ to form fatty
acids and glycerol.

Cleaning in action

When you mop a floor, the soap or
detergent works as hard as you do.
Soap and detergent molecules have a
head that is attracted to water and a
tail that is attracted to grease. When
you mix soap or detergent with water,
the water-loving heads dissolve, while
the grease-loving tails attach
themselves to grease and lift it away
from any surface.

When boiled, sodium
hydroxide reacts with fatty
acids to produce soap.

CLEANING FABRICS
The fibers of a cotton shirt are covered
with grease (left). But when you wash
the shirt, the soap and detergent
molecules attack and remove the
grease clinging to the fibers (right).

Soap curd
forming

Brine dissolvesI
the glycerine.
The soap,
which is
insoluble in the
salt solution,
rises to the
surface of the
vat as a curd.

Sodium

MOLECULE HEADS
Hard water contains
calcium or magnesium
atoms. These replace
the sodium atom in
the water-loving
( head of soap

molecules, forming
a powdery scum.

The vat spins at a
high speed, to
separate the soap
from the brine and
glycerol. These drain
away, leaving pure
soap behind.

Sulfur replaces
carbon in the
water-loving head
of detergent
molecules. This stops
calcium and magnesium,
forming a scum.

Sulfur

Oxygen

Brine and
glycerine ,

Carbon

MAKING SOAP
To make soaps, fats or oils are
heated to break them up into fatty
acids and glycerol. The fatty acids
will react with an alkali, such as
sodium hydroxide, to produce soap.
Brine removes the glycerol from the
soap. Before the soap is made into
blocks, flakes, or powders, chemicals
are added to kill germs, give color
and scent, and soften water.
Manufacturing a bar of soap from
raw materials takes just 15 minutes.

Detergent

WHAT’S IN A DETERGENT?

Most detergents contain enzymes to
break down the molecules in sweat
and bloodstains. Dyes, called
brighteners, make clothes
look brighter. Builders
stop dirt from settling back
on cleaned clothes, soften the
water, and keep the acidity
constant for all the chemical reactions.

Find out more

Phosphorus p.43
Compounds and
mixtures P.58
Solutions p.60
Alkalis and bases p.70
Chemistry of water p.75
Factfinder p.406

MATERIALS

Coal products

When we burn coal, we release energy and chemicals that were
trapped for 250 million years. Back then, huge numbers of dying plants
decomposed slowly to form coal. We use coal to provide the energy to spin
electrical generators in power stations. Heating coal without air turns it
into coke, which provides the energy in blast furnaces for making metals.
When we process coke, it releases other chemicals - ammonia, a
flammable gas, and tar. These can be changed into new
chemicals to produce many different k

products, including dyes, paints, and _ iAaf-

medicine. In fact, more than 2,000 v fW'M*!

chemicals can be made from coal. Idk _

COAI. IN THE MAKING
Swamp plants used the Sun’s
energy, and chemicals in their
surroundings to make chemical
energy in their cells. When the
plants died, their remains
turned into coal.

Coal gas contains
hydrogen, methane, and
k carbon monoxide. It was
WL first used for lighting in
Wk 1792. In the 19th
century, coal gas
■ provided energy for
B§ both lighting and
HF cooking in many towns.

Ammonia gas is dissolved in sulphuric acid
where it reacts to form crystals of
ammonium sulphate. Until 1913, these
crystals were the main source of fertilizers.

From coal to coke mfly

When coal is heated to a
temperature between 900° - ^BjMj

1,300°C (1,650°-2,400°F) in ovens,
without any air, a mixture of gases and
liquids escape from it. These are separated
into coal gas, a watery solution of ammonia
called ammoniacal liquor, and coal tar. The
solid left behind is called coke. It contains
more than 80 per cent carbon.

Ammonia

liquid

A range of cokes are
made by heating
different kinds of coal at
either a low or high
temperature. The cokes
produced provide fuel
for heating in homes
and industries.

COAL TAR CHEMICALS ^

Coal tar contains several
useful chemicals.

These are separated a

by distillation,

because each has a m -H

different boiling
point. Chemicals with
high boiling points
include pitch and creosote.

Those with lower boiling points
include benzene and carbolic acid.

Burning

coal

Carbon

Benzene is a ring compound of
hydrogen and carbon atoms.

Spraying fruit trees
with pesticides made
from coal tar

Hydrogen

USEFUL MOLECULES
The molecules in coal tar form the
raw materials for making hundreds
of new chemicals. By adding other
chemicals to these molecules,
thousands of useful products can
be made. Creosote in its unrefined
state is a wood preservative. If the
different molecules in it are
separated, they can be used for
making pesticides and drugs.

Early dyes made from
aniline - one of the
compounds in coal tar.

Coal tar soap

COLOURS AND KILLERS
In the 1850s, chemists made the
First synthetic dyes from coal tar
chemicals. They were brighter than
most natural dyes, and did not fade
in light or easily wash out of
fabrics. When carbolic acid (a coal
tar chemical) was discovered to
have antiseptic properties, it was
added to soap to kill germs.

Find out more

Carbon p.40
Ammonia p.90
Gas products p.97
Oil products p.98
Dyes and pigments p.102
Fact finder?.406

Pills made from
coal tar

MATERIALS

Gas products

Propane

MIX OF GASES
There are four main
gases in natural gas.
The proportions
vary, but a typical
ratio is 80 per cent
methane, 7 per cent
ethane, 6 per cent
propane, and 2.5
per cent butane.

Methane

The FLAME BURNING on a gas cooker marks the end of a long journey
for a chemical called methane. The trip began millions of years ago, when
the remains of tiny marine plants and animals formed natural gas that
became trapped in rock. Most of this gas is methane, but there are many
other chemicals in it too. In the 1930s, natural gas was cleaned of any
impurities, and we began to use it as a fuel. Chemists soon discovered that
these impurities could be used as raw materials in other industrial plants.
Methane itself is also used as a raw material to produce hundreds of
different products, from fertilizers
to detergents. It can even be
used to make protein. Jfc

Butane

Methane is piped directly to
towns to provide fuel

Ethane

In the extraction plant, methane
is separated from other gases
and any remaining liquids. A

A mixture
of gases and
liquids is piped
from the rig to the
separation plant.

The pressure is reduced,
so that the heavier
hydrocarbons
become liquid.

Liquids are trapped
at the bottom
of the “slug
catcher”.

r Ships transport
liquid methane to
different
~ countries.

Gas separation " x

Impurities are removed from
natural gas in a variety of ways.

When the pressure is reduced, some
of the heavier hydrocarbons become liquid
and separate from the gas. Alcohol removes
water, while special chemicals absorb sulphur
and carbon dioxide from the gas.

In this -nX - - sr-
column, heat
drives ethane to
the top to be piped
away. Other gases and
liquids pass to the next
column.

Heat

drives \

butane to the \ /

top. The remaining ""y .

liquid, natural gasoline,
is piped away from the bottom.

Propane is
piped away
after heat
drives it to
the top.

When ethane is heated, it loses
two hydrogen atoms and

_ turns into a molecule

. ; . ofethene.The

double bond
between the
carbon atoms
\ makes ethene
Jr | much more

j reactive than
ethane. So
/ ethene is a very
useful raw material.

Natural gasoline
is used to make
diesel fuel~^

Butane is
turned into a
liquid and
piped to a
storage tapk.

Propane is
turned into a
liquid and
piped to a
storage tank.

Plastics

The world’s
W chemical industry

produces about 40 million
tonnes of ethene from
natural gas and oil every
year. Ethene reacts easily
with other chemicals, or
even with itself, to form a
range of plastic materials.

Ethane is piped
to a chemical
plant for further
processing. ^

Hr LIQUID GASES
Butane and

propane are pressurized to form a liquid.
When the pressure is released, the liquid
becomes a gas once more. Camping
cookers, lanterns, and cigarette lighters
rely on these liquefied gases.

USEFUL IMPURITIES
The chemicals removed as
natural gas is purified have their
uses too. Sulphur provides the
raw material for making
sulphuric acid. Hydrogen is
used to make ammonia. And
the uses of helium, a very light
and unreactive gas, include
filling balloons and controlling
the pressure of rocket fuel.

Find out more

Carbon p.40
Behaviour of gases p.51
Separating mixtures p.61
Coal products p.96
Oil products p.98
Oil and gas p.239
Fact finder? .406

Plastic ducks and ski
boots are just two of
the many plastic
products formed
from ethene.

MATERIALS

Oil products

Heavy, or long chain,
hydrocarbons are
black, thick, and

Light, or short chain, _

hydrocarbons are pale
and thin.

CRUDE OILS
Oil contains a mixture of
hydrocarbons, each with a

different number of carbon atoms in its chain. The
proportion of hydrocarbons in oil varies from one
place to another. Middle East oil has more long
molecules, which makes the oil thick. North Sea oil
has fewer long molecules and is thinner.

GASOLINE
Between 70° and 160°F
(20°-70°C), a thin, runny
liquid runs out. This is
called gasoline. The
hydrocarbons in gasoline have between five and
ten carbon atoms. Gasoline is mostly used as
automobile fuel, but it also acts as a raw material for
making plastics or chemicals such as detergents.

KEROSENE
A light oily liquid
called kerosene
condenses at
temperatures between
320° and 480°F
(160°-250°C). Kerosene,

with between 10 and 16 carbon atoms, is made
into aviation fuel for burning in jet engines.
Paraffin is used for heating and lighting, and
in solvents for paints.

Fractional

DISTILLATION
When crude oil is
heated to a certain
temperature, the
hydrocarbons in
it turn into
different gases. Each
gas condenses back into
a liquid at a different
temperature. In this way, oil can be
separated into various parts, or
fractions. The separating process is
called fractional distillation. Hot crude
oil is fed in near the base of the column.

The heaviest hydrocarbons condense at
once and fall into the level below. The other
hydrocarbons, still gases, rise through the column
until they cool off enough to condense back into a
liquid (at a temperature just below their boiling point)
They are then piped away for processing.

Oil DOES NOT JUST PROVIDE the power to turn the wheels
of a car, it covers the roads they run on, too. Crude oil is a sticky,
dark liquid that occurs naturally under the ground or sea and has
a pungent smell. Most of the substances found in crude oil are
hydrocarbons: compounds of hydrogen and carbon atoms joined
together in chains. They formed more than 200 million years ago
as the remains of marine plants and animals decayed. Early in this

century, chemists discovered
that they could separate the
different hydrocarbons in
oil by heating them.
Chemists now make
thousands of products from
crude oil.

REFINERY GASES

At 68°F (20°C), only four hydrocarbons remain as
gases. These are methane, ethane, propane, and
butane. Some methane and ethane is used as a fuel
to heat the oil for fractionating, but most is used for
making chemicals. Propane and butane are bottled
as fuel for portable gas stoves and lights.

NAPHTHA
This yellow liquid
condenses at temperatures
between 160°-320°F
(70°-160°C). With 8-12
carbon atoms, naphtha can be made into
automobile fuel, plastics, and chemicals for
drugs, pesticides, and fertilizers. It is also
used as a solvent for processing rubber or
extracting oil from seeds.

GAS OIL

At this level, which is
kept at 480°-660°F
(250°-350°C), gas oil
condenses. It has
between 14 and 20
carbon atoms. Gas oil
is used to make diesel
fuel and central
heating oil. It also
makes asphalt softer
and easier to spread.

Gases pass up the column
through bubble caps. If the
temperature is cool enough,
the gas condenses on the
cap and runs off as a liquid.

Asphalt provides
the surface for
many of the
world’s roads.

RESIDUE
All hydrocarbons
with more than 20

carbon atoms condense as soon as they enter the
column. The mixture of heavy hydrocarbons is
separated by heating to produce lubricating oil,
petroleum jelly, candle wax, and bitumen.

MATERIALS

Breaking up molecules

Separating the hydrocarbons in oil by
fractional distillation gives more
long-chain molecules than we
can use and not enough small J

ones such as naphtha and gasoline.
Catalytic (speeded-up) cracking splits,
or cracks, the larger molecules into
more useful, smaller ones. Cracking
involves heating the heavy oil under
pressure in a special cracking
chamber. Some of the bonds between
the carbon atoms break to leave a
mixture of shorter chain
hydrocarbons. By using a catalyst, the
process is speeded up, and cracking
can take place at a lower temperature.

A 16-carbon hydrocarbon is sent to the
catalytic cracker to be broken into a
mixture of lighter hydrocarbons. After
cracking, the mixture passes to a
fractionating column to be separated.

Industrially,
cracking is
done on a
large scale in
big plants. ^

Inside the cracker

The hydrocarbons, heated by steam,
pass over the hot catalyst of powdered
alumina-silica gel. The catalyst
provides a huge surface on which the
v hydrocarbons break up into smaller,
IfVmore useful, hydrocarbons.

The catalyst is
continuously cleaned
and recycled. _

Powdered catalyst
mixes with the y
hydrocarbon /
in steam _ /

Polyethylene

toys.

The catalyst
becomes dirty
as tar and coke form on
it during cracking.

PLASTICS ^ | - -J2

Heat jCr

ethylene under Of]

pressure, and

groups of between mmT

1,000 and 10,000 Cj

molecules join to make
long-chain molecules of
polyethylene. Polystyrene, used as
packaging, is made by mixing benzene U
with ethylene. One use of polystyrene is
to make safe toys for children. Ethylene and
chlorine make polyvinyl chloride (PVC).

A fragment of
polyethylene

Propylene, three
carbon atoms,
used for plastics

Heptane, seven
carbon atoms,
used for gasoline

Ethylene’s many uses

/ After cracking, the compounds are

separated by fractionation. One of them,
ethylene, is so reactive that it can easilyjoin
with many chemicals, and even other
ethylene molecules, to be converted into a
dde range of useful liquids and solids.

Ethylene reacts with
water to provide a
solvent for paints
and perfumes.

Bromine is
added after
cracking .._

Ethylene

Water is added
after cracking.

Dibromoethane

Ethanol

Find out more

GASOLINE ADDITIVE
Adding bromine to ethylene
produces dibromoethane, which is
used as an octane booster f or
motor fuels. It prevents gas from
igniting too quickly in the engine
and causing “knocking,” which
reduces the engine’s performance.

ETHANOL

Ethylene and water combine to
produce ethanol, a solvent used
for manufacturing many paints,
cosmetics, perfumes, soaps, and
dyes. Adding oxygen to ethanol
produces acetic acid, used in
making synthetic fibers.

Atomic structure p.24
Bonding p.28
Crystals p.30
Rocks and minerals p.221
Fact finder p.406

MATERIALS

Table tennis balls are
still made from
celluloid.

POLYMERS

CELLULOID

By changing the ingredients
of Parkesine, an American
chemist, John Hyatt, made
celluloid. This was used for
making spectacle frames
and photographic film, but
other plastics have now replaced it.

This is
chloroethene,
the monomer
that makes
PVC. The
double bond
makes it very
reactive.

Is THAT A POLYMER GROWING out of your head? The fibres that
make up your hair are made of long, strong, flexible molecules. They
are polymers - long, winding chains made up of thousands of smaller
molecules, called monomers, linked together. Polymers are common
and useful molecules. Natural polymers not only make up hair, but

also the cellulose in plants, and the wool of
sheep. Polymers can also be made from
chemicals. All plastics and many of the
clothes we wear are made in this way. The
first synthetic polymer, Parkesine, was made
by English chemist Alexander Parkes in
the 1850s. Today, chemicals are
made into a wide range of
polymers. They can be
designed for
Hydrogen ^ , particular

jobs.

One of the bonds from the double bond
x breaks in half. One half bonds with
the chain. The other half will link
with the next chloroethene
— molecule that
comes
along.

Chlorine
atom __

This inflatable
snake is made
from PVC, a
thermoplastic.

THERMOPLASTIC
The way that polymer chains are
arranged affects the way a plastic
behaves when it is heated. In a
thermoplastic, the chains are arranged
side by side, with no links between
them. When heated, the chains slide
over each other, and the plastic melts.

It sets again when the temperature falls.

Addition

Have you heard of PVC?

This is short for polyvinyl chloride,
more properly called polychloroethene.

You can tell from its name that the
monomer that makes PVC is vinyl chloride,
although this is now called chloroethene. In

PVC, the monomers are linked up by a
method called addition polymerization.

This just means that one molecule is | \

tacked onto the end of another one. V,

Given the right conditions, thousands of
chloroethene molecules will link up in this
The two O " . O way to make one huge molecule of PVC.

monomers that

make nylon _

IT MB il L The words polymer and monomer come from

each other. ™ f O Greek words. "Poly" means many, “mer" means

part, and “mono" means one.

The delicate
electronic
components
of this
personal
stereo are
protected in
a case
made from
a thermoset.

THERMOSET

Polymers such as melamine and
silicone are thermosets. Their
polymer chains are linked together
to form a strong network. When
heated, the chains cannot move,
and so the plastic does not melt.

PIASTIC PELLETS
Most plastics are produced in the
form of granules or pellets.
Polystyrene granules are
white, polyethene granules
are transparent. When these
pellets are melted, they can be
coloured and made into
whatever object is required.

The released
atoms join to make
a water molecule.

Condensation

Another method of making a
polymer is by condensation. With
this method, a small molecule is
thrown out when the monomers join up.

Nylon, a polymer used to make clothing, is
made in this way. It is made from the linking of
two monomers. Every time one monomer joins
onto the chain, a molecule of water is released.

BAKELITE

During an experiment, American
chemist Leo Baekeland (1863-1944)
found a sticky mess in the bottom
of his apparatus. On heating, this
softened and then set into a hard
solid. He improved its properties
to make a tough, resistant plastic
that could be moulded into
different shapes. He
called it Bakelite.

It was used to
make cameras,
telephones,
and plugs.

100

MATERIALS

Using polymers

Freshly made polymer granules have little use on their
own. But if they are heated, they will fuse together to
make a substance that can be easily shaped. The types of
material that polymers make are very useful because they
are very strong, and yet very light in weight.

Pellets are
fed in here.

EXTRUSION
To make plastic into tubes or sheets, a
r method called extrusion is used Plastic
pellets are taken by a turning screw to
heaters which melt them and turn them
into a thick, sticky liquid. This is squeezed
through a specially shaped hole
called a die to form a tube or a
sheet. When this passes
through a cooler, it
quickly
a inn hardens.

The pellets
of polymer
are fed in at
one end.

Extruding

machine

Moulding

machine

RUBBER

Rubber, a gum extracted from tropical
trees, is a natural polymer. Its molecules
have twists and loops in them which give
rubber its elasticity. Raw rubber is weak, as
its molecules are not linked together. To
make these links, it is heated with sulphur
in a process called vulcanization. This
toughened rubber allows tyres to squash
and stretch without breaking.

Turning screw
takes pellets
through heaters.

Heaters melt
the pellets.

Die shapes molten
plastic into tube. ^

^ Heater

Miles of tubing can be
made by an
extruding machine. 4

Ram pushes
the plastic
pellets
through the
machine.

Heater

Mould for

bicycle

helmet

MOULDING
One way of turning plastic into special
shapes is by a method called moulding. A
ram pushes the pellets through a
^ machine where heaters melt them.
The hot, liquid plastic is then forced
into a mould. Water cools the
mould and makes the plastic set.

Vacuum

forming

machine

Plastic

sheet

warms

under

heater.

Mould

Up to 90 bicycle helmets an hour can
be made on one moulding machine.

VACUUM FORMING
Intricate plastic shapes can
be made from plastic sheets by a
process called vacuum forming. A
plastic sheet is put over a mould and a
heater softens it. When air is sucked
out of the mould by a vacuum pump,
the softened plastic sheet is sucked
into the mould by the air pressure
above. When it is cooled, the plastic
shape can be turned out of the mould.

Sheet is
sucked into
the mould by
air pressure
pushing
from above.

This quick and simple
process makes
millions of plastic
cups every day.

STEPHANIE KWOLECK

An American research chemist,
Stephanie Kwoleck (born
1923) has made many
discoveries about polymers.
. She discovered a solvent that
could make Kevlar aramid
fibre. Its threads are stronger
than steel, yet very light. It is
used to build spacecraft and
bullet-proof vests.

RECYCLING PLASTICS
Some plastics can be recycled.
Polyethene terephthalate (PET),
used for drink bottles, is collected
into bales, cleaned, and then
shredded into chips that can be
used again. Biodegradable plastic
bottles are made from a polymer
of a sugar, glucose. Microbes on a
rubbish tip will break them down
into carbon dioxide and water.

Find out more

Carbon p.40
Organic chemistry p.41
Chemical reactions p.52
Oil products p.98
Fibres p.107
Fact finder p.406

101

MATERIALS

It took 9,000 whelk shells to make
just one gram of purple dye for a
Roman Emperor’s toga.

Dyes and pigments

We LIVE IN A COLORFUL WORLD. Most of the
objects around us have been colored by dyes or
pigments. Dyes color the fibers in our clothes, in
paper, leather, and even food. Dyes can dissolve in
water, so they can get into the nooks and crannies
of a fiber. Here, they bond to the fabric in a
chemical reaction. Pigments are colored particles
that do not dissolve in water. This means they can
only coat the surface of a material and they do not
react chemically with it. They are used to
make paints and printing inks and for
coloring plastics.

Mordant dyeing process

Natural or synthetic

There are thousands of different
dyes. Natural dyes are made
from plants such as indigo, or
shellfish such as the murex
whelk. Synthetic dyes are
made by adding sulfur or
chlorine to the colorless
chemicals made by distilling
petroleum or coal tar.

Metal salts are
mixed with water,
to form a mordant
solution. This
solution is then
heated.

The mordant
clings onto the
fibers by
chemical bonds.

WILLIAM PERKIN
While trying to make synthetic
quinine, William Perkin (1838-1907)
accidentally discovered the
first synthetic dye. He
JM Lt extracted a purple

substance from the
mixture he was working
on and found it could
dye silk. He called it
mauve. Perkin went on to
build a dyeworks. This was
^(BBH^the start of the dye industry.

DYE FAMILIES
Dyes work because their
molecules join onto the material
they are dyeing. Different families of dyes
are suitable for different materials. Direct dyes work
best on fabrics that are only washed occasionally, such
as curtains. Vat dyes are ideal for fabrics that need
frequent washes. Mordant dyes will not color a fabric
on their own. In the mordant dyeing
process, an extra chemical (a metal
compound) fixes the dye
molecules to the fabric.

The cuttlefish is not a fish, but a
mollusk, related to the octopus. Its
ink contains a natural pigment.

The pigments in this
ink are made from
organic chemicals.

PIGMENTS
The cuttlefish
escapes from its
predators by squirting a
cloud of black ink into their
path. The pigment in this ink was
used to give photographs a brown
tint in the 19th century. Today,
however, most pigments are
made from organic chemicals
that give bright colors and do not
fade too quickly.

A chemical bond forms
between the mordant
and dye that holds the
dye to the fabric.

1. Pigment particles give the paint its
color. Each particle in this powder
may be as small as
a millionth of a
centimeter across.

DRYING PAINT
When a surface is painted and
left to dry, the solvent in the
paint evaporates into the air.
This leaves the binder and
the pigment close together.

They react to form a tough
weather-resistant film. Paint
may also contain a white
pigment. This scatters light
back to our eyes, so we
can clearly see the paint
color.

2. The pigment is
mixed with the
binder so that the
particles can
spread out evenly.

Water-

based

paint

Emulsion
paint

Close-up view of
surface being
painted

3. The
paint
flows
into tiny
cavities on
the surface
and is
trapped.

The dye will hold fast, which/

means it will not fade when n

the fabric is washed. FAINTS

All paints contain a
pigment to give them
color. But they also need a
chemical called a binder to
hold the pigment in place and
a solvent so the paint can flow
easily. Some paints have water as
their solvent. Some gloss paints,
however, have a turpentine
solvent. This is why they have
such a strong smell.

4. As
the paint
dries, the solvent evaporates,
bringing the chemicals and
pigments in the paint closer
together.

5. The
binder
holds the
pigment
particles in
place.

Find out more

Bonding p.28
Organic chemistry p. 41
Solutions p.60
Coal products p.96
Cosmetics p.103
Factfinder p.406

102

MATERIALS

Cosmetics

ANCIENT COSMETICS
Fashionable Egyptian women
wore kohl to blacken their hair,
eyebrows, and eyelashes. They
also used malachite powder as
eye- shadow. Kohl is made from
naturally occurring lead sulfide,
called galena. Malachite is made
from ground copper carbonate.

Loose powder, made of
white pigments, gives the
skin a smooth surface.

Liquid cream holds
other cosmetics to
the skin.

BEFORE AND AFTER
Cosmetics were applied to
one-half of this model’s face to
show how they can change a
person’s appearance. The first step
was to apply the foundation cream, to
help keep the makeup in place. Next,
a mixture of peach, yellow, and white
powders was applied to the skin. These
cover marks on the skin, such as blueness
below the eyes or redness caused by blood
vessels close to the surface of the skin.

Emulsifier

As LONG AGO as 5000 B.C., the ancient Egyptians used cosmetics
to change their looks. Their cosmetics were made from ground-up
minerals. The cosmetics we use today are made from a mixture of
chemicals. Many of these come from the petroleum industry. They
are mixed with plants, oils, waxes, talcs, clays, and various metal
compounds. When a new cosmetic is made, great care is taken to
make sure the chemicals it contains do not harm
the skin. There are tighter controls on make¬
up such as lipsticks, as these may
accidentally get into the mouth. In the
past, the chemicals were tested on
animals, but today more companies are
finding new ways to test the chemicals.

Eyebrow shadow
and penci l make
the eyebrows
more striking.

This eye shadow
contains turquoise
pigments to coat
upper eyelid.

Black eyeliner
on the eyelids
make the eyes
stand out.

Mascara contains a
black pigment to
emphasizes the
eyelashes.

Blusher contains brown
and pink pigments to
color the cheeks.

Lip pencil marks the outline of
the lip, and the lipstick
contains pigments that color
the lips to complement skin
and hair color.

Water

Oil molecules
have forces
between them
that prevent
them from
mixing with
water.

Oil molecules are
attracted by the
oil-liking end of
the emulsifying
molecule.

These are some of the
cosmetics you’ll see in
any department store.
Each one comes in a
variety of shades to
match your skin type.

Water
molecules are
attracted by
the water-liking
end of the
emulsifying
- molecule.

ANCIENT TRADITIONS
For many years, people have
colored their skins with substances
from plants, animals, clays, and
minerals. The reasons for doing
this have ranged from showing the
rank of a person in society, to
preparation for a special
ceremony. Today, the people of
New Guinea still keep these
ancient traditions alive.

A s nails are a fairly tough part of
the body, nail polish contains
chemicals that cannot be
used elsewhere. It
i consists of a pigment
in an organic
solvent such
as acetone.

Water\
molecules
have forces
between the
that stop
them from
mixing
with oil.

Emulsifying
molecules link the oil and
water together. This forms an
oil-in-water emulsion.

EMULSIONS
Cosmetics are often made
from oil and water. These do not
mix, but by adding an
emulsifying agent such as
soap, a creamy substance
called an emulsion can be
made. Liquid paraffin and
petroleum jelly from
petroleum, castor oil from beans,
and lanolin from wool grease make up
the oily part of an emulsion.

WHAT ARE COSMETICS MADE OF?
Every cosmetic contains a mix of
chemicals. Nail polish has at least 11
chemicals. 11 usually contains resin,
plasticizer, solvents, and pigments.
Foundation cream contains up to 23
chemicals. It is an oil-in-water
emulsion that contains a complex
mixture of acids and alcohols.

Find out more

Compounds and mixtures p.58
Solutions p.60
Soaps and detergents p.95
Coal products p.96
Dyes and pigments p.102
Factfinder p.406

103

MATERIALS

Chemistry in medicine

Over 200 years ago, a brew containing foxglove
leaves was used to treat people with heart
failure. Many years later, these leaves
were found to contain the drug
called digitoxin. Today,
digitoxin is still used to treat
heart failure.

Chunks of
willow bark

Foxglove

plant

NATURAL DRUGS

The Greek doctor Hippocrates used willow bark
as long ago as 400 B.c. to relieve the pain of his
patients. But it also caused stomach irritation.

The bark contains a chemical called salicylic acid.
In 1893, a German chemist, Felix Hoffman, made
a very similar chemical f rom coal tar, which had
fewer side-effects. This drug is now known as
aspirin. Over 100,000 million aspirin tablets are
taken every year throughout the world.

YOUR BODY IS MADE from thousands of different
chemicals. If these are not working properly, you
become ill. A doctor may treat you by giving you
more chemicals in the form of medicines. This
treatment of illness is not new. Over 2,000
years ago, the people of Ancient
Mesopotamia used 250 different plants
and 120 minerals to treat ailments.
Many of these were still used in the 19th
century, when the chemicals from plants
were put into tablets. But some of these
gave people a second illness, called a
side-effect. Today, scientists are able to
make chemicals similar to the natural
ones. By altering the molecules slightly,
they can prevent side-effects.

Developing a drug

A new drug is made to treat
a specific illness. Up to 30
chemicals may be selected
for the first set of drug tests.
These may have been made
from chemicals in plants, or
chemicals from the
laboratory. The chemicals
are tested for poisonous
effects. For example, they
may break down to form
harmful substances. The
tests take three years and
only very few chemicals
will pass them.

PAUL EHRLICH

The German doctor Paul Ehrlich (1854-
1915) sought a “magic bullet” which would
kill disease-giving bacteria, but would leave
human cells undamaged. He
thought that dyes that could
stain bacteria but not other
cells might be a good
starting point.

The first synthetic drug
he discovered was the
dye trypan red for
treating sleeping sickness.

Ehrlich later found that a
very similar chemical,
salvarsan, could cure syphilis.

TRACKING THE DRUG
The chemicals that pass the first drug
tests are carefully tested on healthy
humans to investigate any side-effects
they may give. Samples of each
chemical are made slightly radioactive,
so that their movement through the
body can be tracked with an instrument
called a Geiger counter.

DRUG TEST
After eight years of
testing, one drug is
selected. One
group of patients is
given tablets that
contain the drug.

A second group is
given placebos
(inactive drugs).
The effectiveness
of the drug can be
assessed by
comparing these
two groups.

HOW DRUGS WORK

Every cell of your body has receptors on its surface.
Some drugs are thought to work by their
interaction with these receptors. Adrenaline is a
chemical your body produces. It makes your heart
beat faster in times of stress. A drug called
salbutamol relaxes lung muscles by joining
adrenaline on the receptors of lung muscle cells.
But another drug called propranolol blocks off
receptors on heart muscle cells. This prevents
adrenaline from reaching the receptors. In this way,
it prevents a heart from beating dangerously fast.

1. Body Receptor Drug

phemical

Message that chemical This drug is helping the
sends to celll body chemical. It is

reinforcing the message
sent to the cell.

Body

chemical

Message that
chemical sends to cell.

This drug is blocking the
body chemical. It prevents
the message from being
sent to the cell.

104

MATERIALS

Chicken-pox
is a disease
caused by
a virus.

_ VIRUSES

Micro-organisms called
^viruses cause diseases such as
chicken-pox and
'mm colds. Because they inhabit
body cells, it is difficult to
create drugs that kill them, yet do not
harm the person. Antiviral drugs work
by blocking the chemicals the virus
needs to reproduce. AIDS is caused by
a very tough virus. 11 may take many
years before a drug can control it.

BACTERIA

Organisms called bacteria cause diseases such as
tonsillitis. They can be killed by chemicals called
antibiotics. Early antibiotics, such as one called
penicillin, were all made from moulds and fungi.
Today, most are created from other chemicals.
There are two main ways in which antibiotics
work. One type prevents the bacteria from
making its cell walls. Another type interferes with
the chemical activities in the cells of bacteria.

Viruses
cannot be
killed by
antibiotics.
Antiviral
drugs
must be
used.

Bacteria
PP' breaking
y? down due to
effect of antibiotic

We feel -

pain \

because

our

nervous

system

sends -■ —
messages
from the

injured part of our
body to our brain.
Anaesthetic drugs are
used to stop these
messages and numb pain.

Extreme anxiety is sometimes eased with drugs.
Chemicals called diazepam and nitrazepam work with
chemicals in the brain. These drugs can be addictive.

Body chemicals

A healthy body makes many
different chemicals that control
the action of the different body
occur

High stress causes the
body to release too much of
the chemical adrenaline. This
makes the heart beat faster, leading
uto high blood pressure. Drugs called
I beta-blockers stop adrenaline from
reaching the heart muscles.

systems. Some illnesses
because the body produces too
much or too little of one of
these chemicals. Many drugs are
chemicals designed to treat a
particular illness. They work
with the appropriate body
chemical to bring the system
back under control.

ANTISEPTICS

Wounds can become infected with
harmful bacteria if an antiseptic is not
applied to kill them. Antiseptics are
able to kill bacteria in many ways. The
alcohol rubbed onto your skin by a
doctor before an injection kills
bacteria by breaking up the protein
that makes up their cells.

In an asthma attack, tiny muscles in the lungs
squeeze the airways, making it difficult to breathe.
When the drug salbutamol is inhaled, the muscles
relax, and breathing becomes easier.

Stress can make the stomach produce
large quantities of acid, which can result in
an ulcer. Anti-acid tablets can reduce the
acidity. Special drugs called H2 blockers
can stop the production of the acid.

FIGHTING DISEASE

1796 English doctor Edward
Jenner performs first vaccination
against smallpox.

1867 English scientist Joseph
Lister discovers first widely used
antiseptic - carbolic acid.

1928 Scottish scientist
Alexander Fleming discovers
that pemcUlium kills bacteria.

This leads to further
developments on the antibiotic
by Florey and Chain.

1932 German chemist Gerhard
Domagk develops first synthetic
drug to kill bacteria (sulfa drug).

1941 Australian doctor Howard
Florey and German doctor Ernst
Chain develop penicillin.

White blood cells are made by cell division
in the lymphatic system. If they do not
divide correctly, cancer cells develop
which produce a disease called
leukaemia. This can be controlled by
cytotoxic drugs that interfere with the
way the cancer cells divide and grow.

Body chemicals are
controlled by glands,
such as the pancreas.
One chemical called
insulin is used to keep a
store of sugar in the liver
In a disease called
diabetes, not enough
insulin is produced. Extra
insulin must be injected.

Find out more

Chemis try of the body p. 76
Viruses p.312
Bacteria p.313
Prima tes p.336
Cells p.338

Internal environment p.350
Factfinder p.406

A disease called arthritis
occurs when the tissues
in a joint become inflamed
and painful. Anti-inflammatory
drugs such as aspirin block off
the body chemical that makes
the joint swell.

105

MATERIALS

Adhesives

RESIN AS GLUE
Liquid oozes from the
cut branch of a pine
tree. This contains a
resin that has been
used as a glue for
hundreds of years.

The yellow car is
stuck to the board
with a strong
epoxy resin.

IMAGINE TRYING TO WALK in your shoes if you did not have
adhesives holding them together. Adhesives have a wide variety of
uses. They range from the sticky substances on the back of postage
stamps and on the flaps of envelopes, to the substances that hold
together the pages of this book, and to strengthen the joints in your
chair. Many different materials are used as adhesives.
The first adhesives came from plants and
animals. In the 19th century, rubber was a
major ingredient in adhesives. Today
polymers are widely used. Every adhesive
sticks because its molecules form bonds
with the objects it is joining together.
These bonds can be as strong as those
that hold together the molecules in a

piece of rock.

Stabilizing molecules
prevent
polymerization
and keep the
glue in its
liquid form.

A TWO-PART GLUE
Some epoxy resins need a
catalyst or a hardener to make
them set. The resin and
catalyst are kept in separate
tubes and mixed together
when needed. The mixture
quickly forms a bond that will
not melt when heated.

EPOXY RESIN

Industries often use epoxy resin glues.
Epoxy resins are chemically
manufactured synthetic glues. They are
popular because they stick a wide range
of materials together and can form very
strong bonds that are resistant to both
heat and weather.

molecule

REUSABLE LABELS

The sticky strip on a reusable label contains thousands of
tiny adhesive bubbles. A few bubbles burst each time it is
stuck to a surface, making it removable and reusable.

Moisture
from the surface
neutralizes the
stabilizing molecules.

HOW ADHESIVES WORK
Acidic stabilizers prevent adhesive molecules from joining
together in the tube. When you squirt the glue from the
tube, it comes into contact with moisture in the air, and on
the surface that it touches. The moisture neutralizes the
stabilizer, leaving the adhesive molecules to join together.
Polymers, which are chains of molecules, form strong, solid
bonds between the surfaces in contact with the glue.

Resin

Catalyst

Thermoplastic glue

This glue is used in model¬
making. It contains
polystyrene molecules
dissolved in a solvent such as acetone. The
solvent evaporates when the glue is
applied to a joint, and the polystyrene
molecules combine to form a bond. If the
joint is warmed, the molecules slide over
each other as the glue melts, allowing the
joint to be reshaped.

Adhesive molecules
begin to polymerize.

Strong
develop between the
ends of the polymer
and the surface.

A photograph of
magnified molecules
joining together in
an adhesive.

Find out more

Changes of state p.20
Catalysts p.56
Separating mixtures p.61
Polymers p.100
Factfinder p.406

106

MATERIALS

Fibers

When you get dressed, you cover your body in clothes
made of fibers. Natural fibers come from the seeds of a plant or
from the fur of an animal. Other fibers are artificial. For
example, nylon is made from chemicals found in oil. The first
clothes were just animal skins. Then, five thousand years ago,
people began to use natural fibers to make strong fabrics. They
spun (twisted) cotton and wool fibers to make threads of yarn.
The first process of interlocking the yarn into a fabric was
weaving. This is still a major fabric-making process today. Later,
the knitting process developed, producing warm, flexible

clothes. During the 19th century,

| people became more aware of

p 'loosely 3 j^HHl|^^how natural fibers were formed
packed fiber, and soon chemicals were beim

which makes r-1

I this material used to make fibers too.

insulator.

A wide range of
petrochemicals
are made into
pellets and
spun into fibers.

Making nylon

Chemicals from oil are the
raw materials for nylon.

/ the liquid forced through tiny holes in the
spinneret, a liquid dispenser, emerges as
molten fibers of equal thickness.

Raw

materials
are heated
to make
molten
polymer.

Molten/
polymer
is forced
through
the

spinneret.

Nylon fibers are
strong and flexible.

NATURAL AND
SYNTHETIC FIBERS ■
The original fibers used
for clothing, such as wool,
cotton, and silk, came from ^
plants and animals. Today
people also use chemicals,
known as petrochemicals, to
make synthetic fibers. These
include polyester, acrylic, and
nylon, which are cheaper and
stronger than natural materials.

The yarn
is wound
onto the
reel.

Polyester - • • '
fibers are
long-lasting.
They are not
very stretchy,
but they do keep
their shape well.

The fibers solidify The fibers

in a cooling bath.

MAKING NYLON

Nylon was the first synthetic material to be made entirely of chemicals.
Nylon pellets are heated to 500°F (260°C) to form a molten polymer
solution. This is forced through the spinneret: a process known as
extrusion. As the polymer comes out of the tiny holes into the cool
atmosphere, they begin to form solid threads of nylon. These are treated
in a special cooling bath, spun into a long yarn, and wound onto the reel.

Closely woven fabric
prevents rain drops from
passing through it.

The fabric is
heated to help the
resin spread and
cover all the fibers.

Threads of rayon
travel around
rotating wheels to
form the yarn.

WATERPROOFING
Wy Fibers in water-repellant
^ clothes are coated in silicone
resin. The fabric is passed
through the resin with the aid of
rollers. Heat is then applied to it
to help the resin coat the fabric
evenly. The resin prevents the
fabric from absorbing water,
making it an ideal material for
raincoats and tents.

The silicone
resin bath
coats the fabric.

CHARDONNET

The French chemist Count Hilaire
Chardonnet (1839-1924) treated
cotton fibers with chemicals and
alcohol, then forced them
through a spinneret. The
alcohol evaporated, leaving
shiny fibers that appeared to
give out rays of light. These
new fibers were called rayon
or “Chardonnet silk” and
became very popular at the
beginning of the 20th century.

RAYON MANUFACTURE
Rayon is a synthetic fiber made from
cellulose in wood pulp. It is a
reconstituted fiber because the original
raw ingredient, cellulose, is broken
down and then reformed. This creates
a superior form of the orginal material:
it is stronger and easier to dye. There
are different types of rayon. The most
important is called viscose.

Find out more

Changes of state p.20
Bonding p.28
Solutions p.60
Polymers p.100
Dyes and pigments p.102
Factfinder p.406

HtHi*

' --

107

MATERIALS

Paper

EARLY PAPER
Making paper from
wood began in
China in about A.n.
105 using the fibres
from the mulberry
tree. But the idea is
thought to have
come from
someone watching
wasps building
their nests from
tiny wood chips.

Making paper

Nearly one third of the earth is

covered in trees. Many of these trees supply us
with paper. The lines you can see in a piece of
wood are called the grain. They are made by
thousands of tiny fibres that the tree produces as
it grows. The tree uses these fibres to carry water
through its trunk and to support the weight of its
branches. In the paper-making industry the fibres
are separated, then joined together in a criss¬
cross pattern to make thin sheets like the one
these words are printed on. Try tearing a sheet of
paper - you will see tiny fibres that have
been stuck together to make it. By
replanting trees to replace those
chopped down for paper, this
supply of raw material should not
run out.

Paper is sent back to the
paper making machine
for recycling.

Most paper comes from forests of softwood trees
such as spruce and pine.

Wood chips are
cooked into pulp

The trees are cut into
logs and transported
to paper mills by road
and rail, or by floating
the logs down a river.

Each log is broken ^
down into chips about
2 cm (0.8 in) long and
0.5 cm (0.2 in) thick.

Wood chips from spruce are
heated with acid, and wood
chips from hardwoods and
pine are heated with alkalis
to release the fibres.

Making paper

Paper is made in a factory
called a paper mill. Wood is
broken into small pieces to
help chemicals to attack it and
release the fibres. The lignin,
which gives the fibres their
strength, is dissolved in hot
chemical liquids. Then
chemicals are added to the
fibres to make the paper
smooth, strong, and opaque.
Sizing, made from rosin or
wax, is added to make the
paper water-resistant.

RECYCLING PAPER
The number of trees, and the
amount of chemicals and energy
used in paper-making can be
reduced by collecting newspapers
f rom homes, notepaper from
offices, and cardboard from
factories. The fibres these contain
are reused to make
more paper products.

Fibres are mixed with fillers,
sizing, pigments, and dyes
into a smooth pulp.

Water is removed
from the liquid pulp by
suction, and by
pressing the paper
between rollers.

Tissue fibres are lifted by a
knife as they roll off the
machine to give tissue its
soft texture.

Rollers remove excess
water and compress
the paper.

Card is made by
a similar
process to
paper.

Paper is sent
back for
recycling.

PAPER PRODUCTS
Types of paper vary because of the fibres
they contain, the chemicals added, and
the way the pulp is treated on the
paper-making machine. There are
two kinds of wood fibre. The first
are cheap, ground wood fibres.
. The second are more expensive,

, chemically prepared fibres.

Stacks of rollers
smooth the surface
of the paper.

Pulp is
drained on
wire mesh.

■ A felt belt
soaks up any
remaining water
in the paper.

The wood finally
emerges as a roll
of paper.

Find out more

Carbon p.40
Acids p.68
Polymers p.100
Dyes and pigments p.102
Fibres p.107
Factfinder p.406

A huge variety of
paper exists, varying
in size, strength, and
uses. Dyes and
pigments are added
to paper to create an
unlimited range of
colours and patterns.

108

MATERIALS

Ceramics

YOU ARE SURROUNDED by ceramics. Many of the
objects you handle every day are made out of a
ceramic material. Ceramics have a range of uses
from making the walls of your home, insulating
cables on overhead power lines, to mending
broken teeth. Ceramics are divided into two
groups. In the first group are materials that are
moulded into their shape before being heated.
Pottery and bricks are examples of this first
group. The second group consists of materials
that are shaped after being treated by heat. m jjp
These include glass and cement. I " (

The shiny glazes on

Strong, weather-resistant clay beads are also

bricks are ideal building made out of clay,

materials. _

POTTER’S Cl AY
Pottery clay is a mixture of
two clays. Kaolin (china clay)
gives pottery its smooth
texture. Ball clay gives the
pottery its strength.

Using ceramics

Ceramics are the hard,
brittle substances made by
firing clay. Clay has been
used to make pottery for
thousands of years. It

Fired
day loses
its water,
forming a tighter,
stronger structure.

INSIDE A KILN

Moist pottery clay is moulded and
then placed in a kiln until it
hardens. Reactions take place in
the clay in which chemicals
separate and then join together
again to form stronger substances.

Water
molecules
in wet clay

was

originally baked in an open
oven, but it is now heated in
a kiln or furnace until it
hardens. New ceramics are
being developed for use in
car and aircraft engines.
These last longer and are
able to withstand very high
temperatures.

Cement holds
pieces of rock
together in a
concrete
mixture.

The porous clay of
a plant pot lets water
evaporate from the
soil and keeps the
plant roots cool. i

Making cement

Clay, chalk, and
water are the
raw materials
for cement.

Raw materials
are mixed to
form a slurry.

The rotary kiln is up
to 182 metres (600
feet) long and heats
the clay mixture.

Glass is a hard,
transparent
material made
from metal
silicates. It is
shaped from a
molten state.

The glazed surface of
a tile is easy to clean.

Lumps of
cement
(clinkers) are
cooled.

Gypsum is added
to the clinkers.

Cement setting process

Crockery holds
your drink
because
it is watertight.

A mixture ot sand
and gravel

Clinkers are ground with
gypsum to stop the cement
setting too quickly.

Cement is added
to the sand and
gravel.

Water is added,
transforming cement
particles into
crystals.

The end product:
powdered cement

Find out more

SETTING CEMENT
Calcium silicate and
aluminate form crystals when
mixed with water. In concrete, the
crystals grow in the spaces between
the sand and gravel. As the crystals
grow, they surround the sand and
gravel forming strong bonds to
hold the cement together.

MAKING CEMENT
Cement is also a ceramic. During the
cement-making process, calcium oxide
forms from the chalk as the slurry is
heated. This joins with silicon and
aluminium in the clay to form calcium
silicate and aluminate. The clinkers are
ground up with gypsum to stop the cement
setting too quickly for the builders to use.

Changes of state p.20
Bonding p.28
Organic chemistry p.41
Materials p.81
Dyes and Pigments p.102
Fibres p.107

The concrete sets
as the crystals bind
the sand and
gravel together.

MATERIALS

Glass

Calcium

carbonate

Waste

glass

HAND-MADE GLASS
To make glass by hand, molten
glass is collected onto the end of
a hollow blowing iron and a
small bubble is blown. The glass
is then cooled by rolling it on an
iron slab and it is shaped with
tools. The glass is reheated
during shaping, so it is easier
. .j to handle.

Sodium

carbonate

ONE OF THE OLDEST ARTIFICIAL MATERIALS, glass
was first made around 5,000 years ago. Glass is actually cooled
liquid sand. Like thick syrup, it is a liquid that has never set -
an old sheet of glass is always slightly thicker at the bottom
than at the top. Glass is very useful as it is easily shaped, rust¬
proof, and forms hard, transparent objects that are not
affected by chemicals. It is also very cheap to make and can
be recycled over and over again. Glass has a wide range of
uses from holding our drinks to helping us see. Its properties
can be changed by adding chemicals, by adding other
\ a gob is materials such as wire, and by controlling the way

\ dropped into . . . glass COOls down.

WlLjhe mold. Compressed air 5

forces the glass
into the shape of
the mold.

RAW MATERIALS
Sand usually melts at
3,090°F (1,700°C). But
if it is mixed with
sodium carbonate
(soda), the melting
point is reduced, saving
energy. Calcium
carbonate (limestone)
is added to stop the
glass from dissolving in
water. Waste glass
is also added, and
melted down
for reuse.

The raw
ingredients
of glass
are fed
into the
furnace.

The finished Molding process

glass bottle is
removed from
z>^its mold.

BOTTLE MAKING
To make special shapes from
molten glass, a mold has to be used.
A bottle, for example, is made from
a lump of molten glass called a gob.
This is dropped into a mold and
forced into the bottom of it by
compressed air. The tough shape of
the bottle is made by blowing air
upward through the gob. This is
then transferred to a second mold,
where it is blown again to form the
final shape of the bottle.

heated up to
2550°F (1400°C) to
melt the raw materials.

Float glass

It is very difficult to make
sheets of glass for windows.

One method is to flatten the glass
between rollers, but this produces an
imperfect sheet. A very clever way to make
perfectly smooth glass is by the float glass
method. Molten glass is floated on top of
a “river” of molten tin. The surface of the
glass becomes as smooth as the surface of
the molten metal. Rollers carry the glass
to be cooled and hardened.

Float glass process

oxygen.

tin would react with the oxygen
and make the glass surface uneven.

Continuous
7 sheet of
cooled
x. glass

Very thin glass fibers are used in heat and
sound insulation and for strengthening plastics.

Chemicals make glass
colorful. Selenium
sulfide makes it red,
copper oxide makes
it blue, phosphates
and alumina
make it

milky,, mg — aft. ^

s' y' The glass

\y is cut into

lengths with a
diamond-tipped cutter.

The glass
is cooled
slowly so it does
not break.

CHANGING
GLASS
The way glass is
treated after it has
emerged from the
furnace changes its
properties, making it
suitable for a particular job. By
rapidly cooling the glass with jets of
air, toughened glass suitable for car
windows can be made. The green
tint in raw glass can be removed by
adding cobalt and selenium oxide.

Cooling unit

Find out more

Changes of state p.20
Semimetals p.39
Fibers p.107
Material design p.11 1
Reflection p.194
Fact finder p.406

Boron oxide is added to the
raw materials of glass, to
\ make borosilicate glass.
]This is used in oven dishes
) and laboratory glassware
because it is able to resist
temperature changes.

MATERIALS

MATERIAL DESIGN

Imagine what your home would look like if everything were made
out of just one material, such as steel. A wide range of materials need to be
used in the home. A window frame is made from wood for strength, while
the window glass lets in light, but keeps out rain. Today, the wood may be

replaced by plastic, and two panes of glass are often used to _

stop heat escaping. People are always looking for

new

materials to make life easier and cheaper. This search may
involve using an old material in a new way, joining different
materials together, or experimenting with chemicals to
make a completely new material. Every new material or new

combination of materials must be thoroughly ___

tested to check whether it , ~~

can stand up to the /T\

job. ________-X

GLASS-REINFORCED PLASTICS
If glass fibers are embedded in
plastic, they reinforce it and give it
extra strength. This glass-reinforced
plastic, known as fiberglass, is used
to build boats. It is an example of a
composite material, in ft"
which the properties of
two common materials
are combined. x>

Because of composite
materials, these large
satellites can hurtle into
space. Here, they can
transmit signals to a
precise point on Earth.

The body of the satellite is made from
a core of a plastic or metal honeycomb
structure. Strong adhesives join this on
either side to thin sheets of plastic,
reinforced with carbon fibers.

The covering plastic is stuck to
this side of the adhesive film.

The many
antennae work
like mirrors, A

focusing any
signals that reach
them. In this way,
they receive
and transmit JBn
signals from
Earth. jgS

Film of adhesive

Metal or plastic
honeycomb /
core . /

x/f K Satellite material

\A/ If you need to send
something into the harsh

Xl / conditions of space, it _

\ \j\ / must be built out of a JjflBfc

\ / material much flj

\ / more resilient

\. x than wood or K

metal. Satellites are j

jr -made from specially 1 j|i

developed materials. These
are light enough to be launched but can
withstand the stresses and strains produced
when the satellite is put into orbit.

Antenna

HEAT-RESISTANT MATERIALS
Extra-tough materials called cermets can
withstand incredible heat. They are made
by mixing metal and ceramic particles.
Cermets are shaped into jet turbine
blades and rocket nozzles, both of which
get extremely hot in use. More than
30,000 cermet tiles protect the space
shuttle from the frictional heat produced
as it re-enters the Earth’s atmosphere.

SEEING STARS

Enormous telescopes are needed to explore

the vastness of space. The light they

collect must be reflected from

a huge mirror, to make an

image that astronomers

can see. The mirror is j

made from glass mixed

with ceramics. This

gives a material that is

strong, so it does not

break under its own

weight, and does not *■" T

change shape as the

temperature changes.

LIFE-SAVING MATERIALS
Many damaged or diseased
body parts can be replaced by
synthetic materials. Metal alloys
are used to make skull plates.
Artificial hip joints are made
from a combination of metal
alloys and plastics. Blood vessels
are made from fibers of fabrics.
Today, even artificial hearts are
made from a combination of
plastic and aluminum.

Find out more

Properties of matter p.22
Alloys p.88
Fibers p.107
Paper p.108
Ceramics p.109
Glass p.1 10
Fact finder p.406

111

MATERIALS

COVERING EYESORES
Quarries near towns can be filled in
with rubbish. This is stored on
polyethene sheets to control the
drainage of water. The methane
produced by the decaying rubbish is
collected in pipes and used as a fuel.
When the quarry is full, the rubbish is
covered with soil and appropriate plants
to create new habitats for animals.

Industrial pollution

The price we pay for using so many different types of material is
pollution. This occurs when we release substances into the
environment which harm living things as well as structures. Up until
about 200 years ago, there was very little pollution. The population was
smaller and people used mostly natural materials. Their wastes could
be broken down by microbes in the soil. Today, some
our machines, factories, and power stations disfigure
the environment. Some of our wastes do not break
up but pollute the land, the water, and the air.

Industry is now trying to limit the pollution

it creates.

Many of the substances
in waste water can be
used as raw materials
for other industrial
processes.

Solid particles in smoke can be
removed in chimneys by
an electrostatic filter.

The particles collect
on the chimney

OZONE LAYER
Chemicals called CFCs in aerosols and
refrigerants destroy ozone when they
escape into the atmosphere. These are
now being replaced with carbon
dioxide, and with hydrocarbons that
do not destroy ozone.

The amount of sulphur dioxide in
' 3 can be reduced by using
uel which has had sulphur
removed from it or by
spraying the smoke
with water
before it leaves
the chimney.

Using lead-free
petrol reduces
the amount of
lead pollution in
the environment.

Making
pollution

Industrial pollution
takes many forms. Raw
materials are extracted
from the ground, destroying
vegetation and animal habitats,
and leaving enormous holes.
Unwanted solid wastes can form
heaps the size of small hills. The smoke
from factory chimneys produces acids in
the clouds and mixes with exhaust gases from
road traffic to produce smog over cities. The
water released from factories can contain wastes that
kill aquatic life. Oil slicks may be created when ships are

involved in accidents.

Find out more

Sulphur p.45
Catalysts p.56
Chemistry of air p.74
Chemical industry p.82
Biosphere p.370
Factfinder p.406

RECYCLING MATERIALS
Fewer raw materials need to be used if
materials are recycled. This conserves raw
materials for the future, reduces pollution,
and saves energy. Using recycled materials
to make aluminium cans, for example,
would give a 95 per cent saving in energy
and a 95 per cent fall in pollution.

CONSERVING HEAT
If heat is wasted, more
fuel has to be burned to
replace it. This causes
extra pollution. The
loss of heat energy from
a building or factory
can be revealed by an
infrared photograph.
The regions losing the
most heat, hot spots,
show up as white. They
can be treated with
extra insulation to stop
the heat escaping.

False colour image
showing the heat lost
from an office block

112

FORCES and ENERGY

FORCES IN BUILDINGS

Buildings must be made to withstand large forces
or they would fall down. The roof of the terminal
atjeddah airport in Saudi Arabia is made of
fibreglass, which is even stronger than steel.
Forces stretch the roof into an unusual shape.

Energy MAKES THINGS HAPPEN, from a bolt of
lightning to tying a shoelace. Nothing could live or move
without energy. Animals use energy to walk and run;
plants use energy to grow. Winds use energy when they
blow; waves use energy when they roll across the ocean.

And when a car moves, it is using energy stored in its fuel.
But none of these things would happen if there were no
forces at work. Whenever energy is used, forces are involved.

Forces are needed to start things

moving, to change the way they
move, and to stop them from
moving. Forces are also
responsible for breaking
things and for holding
things together. Without
forces and energy,
nothing would happen
in the Universe.

SPACE
Forces
and energy
act on a huge
scale in space.

The stars shine
because they are
producing energy in
the form of heat and
light. The atmosphere
of a star is kept in place by
the force of gravity - the
same force that pulls objects
towards the Earth.

ENERGY FROM THE SUN
The Sun provides most of our
energy in the form of sunlight.
More energy reaches Earth from
the Sun in an hour than all of us
use in a year. Plants like these
sunflowers need the Sun’s energy
to grow. They store some of it in
chemical form. An animal that eats
a plant uses this stored energy.

NIGHT LIGHTS

Electricity is a form of energy. It can be
generated in large power stations and
transmitted long distances by cable to
homes, offices, and factories. A flick of
a switch easily changes it into heat and
light energy, and mechanical power.

Subatomic forces

Tiny particles are influenced by
forces just as large objects are.
The forces that act inside the
nucleus, or centre, of an
atom are the strongest of
all forces. Their energy
is released in a nuclear
bomb explosion.

USING
THE WIND
Windsurfing involves the use of
forces and energy. Windsurfers use
their own energy to control the
board and leap over the waves. The
wind’s energy creates the force that
blows them along. But if there is too
much force in one direction, the
board will overturn. Windsurfers
must therefore exert a force against
the wind so that they can balance
and keep the sail upright.

Forces act on particles
that can be seen only
under a microscope.

113

FORCES AND ENERGY

FORCES

THERE ARE FORCES all around us. A force is a push or a pull. It is
something that acts on an object. The wind exerts a force when it blows;
gravity is a force that pulls everything down towards the centre of the
Earth and gives objects their weight. Animals and machines make forces
too. When a grasshopper leaps from a leaf, its legs exert a small force on
the leaf. Machines are used to produce large forces. A jet engine can
produce a force that is millions of times larger than the force produced
by a leaping grasshopper.

FORCES IN FLIGHT
An aeroplane in flight has four
forces acting on it. The
engine produces a
forward force called thrust,
the wings produce an
upward force called lift, and
the force of gravity pulls the
aircraft downwards. A force
called drag, caused as the
aircraft pushes against the air,
slows it down.

Forces acting in
pairs can twist
materials. _ _ _

Forces can
stretch an
object.

Pairs

of forces can
bend an object.

J / Forces
can stop a
moving object
or make it slow down.

' Forces can
make a moving
object swerve and
change direction.

Forces can make \
an object move, \
and make a
moving
\ object go
v—s. \ faster.

J/ \ Forces can

--^ \ make a moving

\ object bounce.

Forces can make \
s \. an object sink \.

\ or float in a
— liquid.

Effects of forces

k J If a force pushes or pulls something, there
^ / are four main things that could happen. A
/ stationary object might start to move, the speed
of a moving object might change, the direction of
a moving object might change, or the shape or size
of an object might change. The greater the force,
the greater the effect it has.

Forces can M
squash or
deform an object.

FORCE FIELDS

The region in which a
force can be felt is
called a force field. The 4
strength of a force field
is greatest close to its
source, such as a magnet.
Iron filings scattered on
a piece of paper on top
of a magnet will gather
along the lines of force
in the magnet’s force
field. The lines show how
the force field spreads
out around the magnet.

FORCES OF

NATURE

Some weather

conditions create

strong forces. A tornado, a

whirling spiral of wind, can

cause a huge amount of damage.

Large tornadoes toss anything in their path -
cars, buildings, trees - high into the air and
then smash them down hundreds of metres
away. The most destructive tornado on record
occurred in the United States, in 1925.
Hundreds of people were killed as it lef t a
300 m-(980 ft-) wide trail of
demolished buildings, uprooted
trees, and overturned cars. A

114

FORCES AND ENERGY

ABDUS SALAM

In 1979, the
Pakistani scientist
Abdus Salam
(born 1926)
became the first
person from his
country to receive
a Nobel Prize.
Salam had wanted to be a civil
servant but changed his mind when
he won a scholarship to study
physics at Cambridge University,
England. At Cambridge, he
developed the theory of the
electroweak force. His ideas were
proved correct at CERN, the
European research laboraratory
near Geneva, Switzerland, in 1973.

The second ball starts
to move only after a
force has been applied
by the first ball.

HITTING
WITH FORCE

When a snooker player hits the ball

with the cue, a good contact is essential. The

push of the cue applies a contact force to the ball. If the

moving ball hits another stationary ball, the contact starts the

second ball moving.

ELECTRIC FORCES
A plastic ruler can be given an
electrical charge, called static
electricity, by rubbing it against
a T-shirt or a jumper. The static
electricity will cause the ruler to
attract small pieces of paper to
it without touching them.

The more force used to hit
the ball, the further the
ball will go.

The Earth is a
huge magnet.

Its magnetic
force makes
compass needles
point northwards.

Contact and non-contact forces

Some forces are only produced when one object
touches another. These are called contact forces.
Other forces do not need contact to have an effect.
For example, a magnet can pull a piece of iron
towards it without touching it. These forces
are called non-contact forces.

ELASTIC FORCE

In the pole-vault, the athlete is helped over the bar by the
elasticity of the pole. The athlete plants one end of the pole
on the ground and bends the
other end down. As the pole
straightens it applies a force to
the vaulter, lifting him
upwards. The
vaulter and pole
obviously need to
be in contact with
each other!

BASIC FORCES
The basic forces
are gravity,
electricity,
magnetism, and two
kinds of nuclear force
called the weak and strong
forces. All other forces come
from them. In 1979, Sheldon
Glashow, Steven Weinberg, and
Abdus Salam received the Nobel
Prize for Physics for proving that the
magnetic, electric, and weak nuclear
forces are really aspects of one force.

They called this force the electroweak
force. Scientists are now trying to prove
the theory that gravity and the strong
nuclear force are related to the electroweak
force. This theory is called the Grand
Unified Theory, or GUT.

The heat and light
energy released by
the Sun comes from
the nuclear forces
of its atoms.

The solar panels of a
satellite produce
electricity from the
Sun’s light.

Static electricity makes
small pieces of tissue
paper jump up and
stick to the

Gravity is a long¬
distance force. The
Earth’s gravity
reaches far into
space and keeps
satellites in orbit.

- Find out more -

Forces and motion p.120
Energy sources p.134
Nuclear energy p.136
Static electricity p.146
Magnetism p.154
Structure of the earth p.212
Tornadoes p.259

115

FORCES AND ENERGY

Resultant

To find the resultant of
several forces, the
direction of the
forces must be
taken into
account as well
as their size.

When two
forces act at
an angle to
each other,
the resultant
lies between
them.

Combining forces

MANY OBJECTS ARE ACTED ON by more than one force.
For example, a yacht’s weight pulls it down but the water
produces an equal upward force, which stops the boat sinking.
The wind blows on the sails to push the yacht through the
water, but the water pushes back on the hull and slows the
boat down. The overall result of two or more forces
acting on an object is called the resultant force. The
resultant of two forces is a single force, which has
_ the same effect as the two forces combined. wind

tr (vnl Forces are what are called vector

quantities. A vector quantity has a
direction and a size.

PARALLELOGRAM OF FORCES
When two forces act on an object in different
directions, with an angle between them, the
resultant can be found by drawing a

parallelogram. Sides A and B
represent the size and direction
of the forces; sides C and D
are drawn parallel to A and
B; then the line E indicates
the size and direction of
the resultant.

Two teams of
Ancient Egyptian
workers hauling a
block of stone
produce two
forces at an angle
to each other.

The resultant
causes the block
to be dragged
forwards.

When two magnets exert
equal and opposite forces
on steel ball bearings, the
bearings stay still and do
not move towards
either magnet.

FORCES IN SAILING

Sailors can make their boats go in any
direction, no matter which way the
wind is blowing. This is because two
forces combine to produce a
resultant that drives the boat in the
required direction: the force on the
sails, which depends upon the
direction of the wind and the position
of the sails; and the force produced
by the keel, which stops the boat
being blown sideways.

WEIGHTLIFTING
If two forces acting on an object in
opposite directions are different sizes,
the resultant will be in the direction of
the larger force. A weightlifter strains to
give an upward force to a bar. But the
weight of the bar pulls it down. The
upward force created by the weightlifter
has to be larger than the downwards pull
if he is to lift the bar higher. If the weight
of the bar is the larger force, the bar will fall
back to the ground.

PULLING
TOGETHER
WTen forces pull in
the same direction, the
resultant can be found by
adding the forces together.

Two train engines pulling
together in the same direction
combine their forces. The
resultant force is double the force
of a single engine.

EQUAL AND OPPOSITE FORCES

If two forces pull an object in opposite
directions, the size of the resultant can
be found by subtracting one force
from the other. If the forces are
equal, they balance each

other. The resultant will be
zero and the object will
not move.

Find out more

Flo a

Forces p.1 14
IRCES IN FLUIDS P.l
TING AND SINKING

Magnetism p.1 54
Factfinder p.408

p.129

116

FORCES AND ENERGY

Balanced forces

If NOTHING HAPPENS when a force acts on an object, it
means that the force must be balanced by another force. For
example, during a tug-of-war, the teams may both heave away
but have no effect - the rope stays in the same position. This
is because the teams are equally strong and are pulling in
opposite directions with the same force. The forces cancel
each other out and produce a zero resultant. The object is
said to be in equilibrium. If you sit on a chair, you are
pushing down on the chair with your weight. If the
chair does not collapse, then it must be pushing
upwards with a force equal to your weight.

If one rope breaks, the
balance is upset
and the tent will
collapse.

In a simple
bridge, the
weight is
supported
tthrough upward
forces produced
by the supports.

BUILDING BRIDGES
Bridges need to be built so
that they support their own
weight and the weight of
heavy traffic without
collapsing. These downward
forces must therefore be
balanced by upward
forces. The simplest
bridge is the beam
bridge. It is
supported at each
end. In an arch
bridge, the curve of the
bridge structure transfers the weight
to the supports at each end. In a
suspension bridge, the weight is
supported by upward forces from
the cables as well as the towers.

Beam bridge

Arch bridge

TUG OF WAR TENT
When a tent has been
put up properly with
guy ropes pulled
tight all the way
round, the tent
should not fall over.
The ropes along one
side of the tent pull in
the opposite direction to
the ropes on the other side
and the pulls balance each other.

Suspension bridge

If three forces are in
equilibrium, a scale drawing
of the forces forms a
triangle. The sides of the
triangle show the size and
direction of the forces; the
directions must all be
clockwise or anticlockwise.

The towers pull some of
the weight sideways as
well as supporting
it vertically.

Weight pushing
down is
supported by
upward forces.

CARRYING A LOAD
To carry a log, an elephant must
lift it straight up with its trunk with
an upward force exactly equal to
the log’s downward force, or
weight. Two opposite forces cancel
each other out if they are equal
and in line.

FORCES IN BUILDINGS

Architects design buildings so
that the forces on the walls
and foundations are in
equilibrium, otherwise the
buildings would collapse.

Many cathedrals have flying
buttresses - structures that
reach out from the outer
walls and down to the
ground. They help the
walls to support the huge
weight of the roof. The
buttresses of Le Mans
Cathedral in France are
more complex than most!

STRONG TRIANGLE
The triangle is the strongest shape
to build with. It is the only shape
that does not twist and collapse
when under pressure. Many
buildings and bridges are based on
triangle shapes. The triangle
sections in this radar dome allow
the dome to be made of fibreglass
which, unlike concrete, is
transparent to radio waves.

Find out more

Material design p.1 11
Forces p.114

Forces and motion p.120
Gravity p.1 22
Turning forces p.1 24
Radio p.1 64

117

FORCES AND ENERGY

Speed

When we say that a car is travelling at 50 km
(31 miles) per hour we mean that the car will take
one hour to travel 50 km (31 miles). This is true
only if the car keeps going at a constant speed - the
same speed all the time. During a real journey, a
car will slow down sometimes and go faster at other
times. It is therefore useful to calculate the average
speed. If you travelled 200 km (124 miles) in two
hours, your average speed would be 100 km
(62 miles) per hour - distance travelled divided by
time taken. In science, speed has no particular
direction. It is known as a scalar quantity. Speed in
a particular direction is called velocity. Velocity is a
vector quantity.

RF.I ATIVE SPEED
Two moving objects have a
relative speed - the speed at
which one seems to move
when seen from the other.
Two cars racing at the
same speed have a
relative speed of zero.

Spring turns the
pointer back
when the car
slows.

Pointer

Jet aircraft - 3,529 km/h
(2,192 mph)

Fastest high-speed train -
515 km/h (320 mph)

Thrust 2 - holder of the land
speed record - 1,019 km/h
(633 mph).

DIFFERENT SPEEDS
Light travels so fast - at
300,000 km per second
(186,000 miles per second) - it is
difficult to imagine it. A sloth, an animal
from South America, moves so slowly - at
about 2 m (7 ft) per minute - it is difficult to
actually see it moving. Here is a selection of
things that move at different speeds.

THE SPEEDOMETER
A speedometer in a car
shows instantaneous speed
- the speed at which the
car is travelling at any
instant. The speedometer
is driven by a cable that is
connected to the shaft that
'drives the wheels.

Cable

rotates with

the wheel

shaft at road

speed

Magnet
rotates with
the cable.

Drag cup, rotated
slowly by the magnet,
turns the pointer.

Bird in level flight -
90 km/h (56 mph)

Dial

Racing powerboat -
166 km/h (103 mph)

Sports
car -
325 km/h
(202 mph)

Cheetah

- 96 km/h
(60 mph)

FINISHING TIME
As athletes finish a race, they pass in
front of a photo finish camera. The
camera takes a picture of them against
a computerised clock accurate to one-
thousandth of a second. The
developed picture shows who won the
race and in what time. It is a picture of
a small area taken over a period of
time - the time i t takes f or all the
competitors to finish.

Human -
36 km/h
(22 mph)

Rabbit -
40 km/h
(25 mph)

ALBERT EINSTEIN

Born in Germany,
Albert Einstein (1879-
1955) was one of the
greatest scientists of all
time. He developed
the theory of relativity.
He became Professor of Physics at the
University of Berlin, and received the
Nobel Prize for Physics in 1921. Einstein
left Germany in 1933 and settled in the
United States. He developed the special
and the general theory of relativity - the
basis for our ideas about the universe.

THEORY OF RELATIVITY

In 1905, Einstein published his theory of relativity,
which described how time seems to run slowly on
something moving at near light-speed, and nothing can
move faster than light. A clock on a train moving at
near light-speed would seem, to a person outside, to be
running slow. Einstein also discovered that matter can
be converted into energy. This is the source of energy
in an atomic explosion and a nuclear reactor.

Snail - 0.05 km/h
(0.03 mph)

NA)

n/h

Find out more

Combining forges p.1 16
Acceleration p.1 19
Nuclear energy p.1 36
Light p.1 90
Photography p.206
Life cycle of stars p.280
Movement p.356

118

FORCES AND ENERGY

Acceleration

When a car changes speed it is

said to be accelerating. When you are
travelling in a car, you can feel if the car
accelerates suddenly - you get “left
behind”. The car accelerates when the
driver puts a foot on the accelerator. The
further the pedal is pushed down, the more
the car accelerates. Acceleration is a measure
of how quickly velocity increases. If velocity
decreases, it is a negative acceleration called
deceleration. Acceleration and deceleration
happen when an unbalanced force acts
on an object.

The ball rolls
backwards
when the
saucer is
accelerated
forwards.

The ball rolls
forwards
when the
saucer is
accelerated
backwards.

USING ACCELERATION

Pilots of modern aeroplanes have an autopilot to help
them fly the plane. It contains an accelerometer, which
senses if the plane’s velocity - vertically or horizontally
- has changed. If the plane accelerates in one
direction, part of the accelerometer moves in the
opposite direction - a bit like a ball on a saucer. A
computer detects the movement and puts the
plane back on course.

CD03Q3

At 48 km/h
(30 mph)

9 m
(30 ft)

14 m
(46 ft)

23 m
(76 ft)

At 80 km/h
(50 mph)

15 m
(49 ft)

38 m
(125ft)

53 m
(174 ft)

At 118 km/h
(70 mph)

21m (69 ft) 75 m (246 ft)

96 m (315 ft)

Thinking

distance

Braking

distance

Total stopping
distance

STOPPING DISTANCES

Motor vehicles need to be able to accelerate
and decelerate quickly to be safe. Good
brakes are particularly necessary. The faster a
car is going, and the heavier it is, the more
difficult it is to stop. The shortest stopping
distances for an average car in an emergency
stop are shown here. Thinking distance is
how far the vehicle travels before the driver
reacts and uses the brakes. Braking distance
is how far it travels while it slows. At 118
km/h (70 mph), the total shortest stopping
distance is longer than a football pitch!

TERMINAL VELOCITY
A falling object, such as a
skydiver, accelerates as it
falls. Earth’s gravity
accelerates all falling
objects downwards at the
same rate - 9.8 m (32.2
ft) per second, per second.

(They get faster by 9.8 m
[32.2 ft] per second, every
second.) But an object
cannot really fall freely. Friction
between it and the air, called air
resistance, acts against the gravity. Air
resistance increases as the object falls
faster, and when it equals the force of
gravity, the object stops accelerating and
falls at a steady speed. This is called
terminal velocity.

Terminal
velocity for a
skydiver falling
in a flat
position is
about 190 km/h
(118 mph).

An open
parachute
increases the air
resistance which then
equals gravity at a much
slower speed.

The ball bounces __

less high each time
because it gradually
loses energy.

The ball is bouncing
from right to left.

BOUNCING BALL

A bouncing ball accelerates as it falls and
decelerates as it rises. On the way down, the
ball goes further each tenth of a second; on
the way up, it goes less far each tenth of a
second. At the maximum height of each
bounce, the ball is stationary for an instant.

DRAG RACING

Acceleration is calculated by dividing the increase in
velocity by the time taken to reach that velocity. It is
measured in units such as kilometres per hour per
second. For example, in a drag race, a car can
accelerate from 0 to 476 km (296 miles) per hour in
4.88 seconds (97.5 km [60.6 miles]
per hour per second). The
driver has to use a
parachute to make
the car decelerate
and stop before it
reaches the end
of the track!

At the top of
the bounce, the
velocity of the
ball is zero.

Find out more

Speed p.1 18
Friction p.121
Gravity p.122
Measuring forces p.1 23
Work and energy p.1 32
Rockets p.299

FORCES AND ENERGY

FORCES and MOTION

Once AN OBJECT IS MOVING, it will keep moving
until a force halts it. This is proved by spacecraft. They will
travel for ever through space at a constant speed until a force acts on
them. It has taken people more than 2,000 years to understand this.
The Ancient Greek thinker Aristotle thought that an object could only
move if pushed by a force, and the movement stopped when the force
was removed. But this did not explain why a ball continued to
fly through the air after it had left a thrower’s hand. A better

theory was put forward in the 16th century m
inertia by Italian experimenter Galileo. He jfl

ke the bob start to recognized that no force was needed to jf

i they have to keep keep an object moving, only to start, j|

,g to make it move 0 T accelerate j t I n 1687, M

us tendency of the \

gh to resist having Englishman Isaac Newton built upon - m
its state °f motion Galileo’s work. He put forward i

ed is called inertia. 1 / H

objects have inertia three lu.WS OI mOtlOFI. M m

7^&>\IN THE AIR

When you throw a
Yi-X ball, it moves in
two ways at the
same time: forwards at a constant
speed and downwards due to
gravity. The resultant path it takes
is caused by a combination of the
two motions.

The force which lifts
the frog into the air
is accompanied by
an equal and
opposite reaction
force which drives
the lily leaf
backwards.

The frog will stay
still unless an
unbalanced
force acts on it..

The frog’s leg
muscles exert a
force that
pushes the frog
into the air.

if NEWTON’S

THIRD IAW
The third law states
that if you push or pull
an object, it will push or
pull you to an equal extent. As
Newton put it, “to every action there
is an equal and opposite reaction”.

NEWTON’S FIRST LAW
A frog leaping from a lily pad
illustrates Newton’s Laws of
Motion well. Newton’s first law
states that if an object is not being
pushed or pulled by a force, it will
either stay still or move in a
straight line at a constant speed.

NEWTON’S SECOND LAW
Newton’s second law states that when a
force acts on an object the object will
start to move, speed up, slow down, or
change direction. The greater the force,
the greater the change of movement.

MOMENTUM

A moving object has CP

momentum - it will
keep on moving until i
a force stops it. When 9

you catch a ball, you
must exert a force on
it to remove its
momentum and stop
it moving. But when H

'your hand and the flnH

ball collide, the ball
will exert a force on
your hand so the H

momentum of your
hand will change.

The momentum gained by your

ISAAC NEWTON

One of the greatest scientists of all
time, Isaac Newton (1642-1727)
was born in Lincolnshire,

England. He was sent to study at

Cambridge University in 1661. But

during the years 1665-6, Newton

returned home because Cambridge f r

was struck by the Plague. It was then

that he made his most important

discoveries. He formulated his laws of motion and

invented a kind of mathematics, called calculus, to

The best way to catch
a ball is to recoil with
. it so that the collision
ft lasts longer and the
force is less.

Forces p.1 14
Acceleration p.1 19
Gravity p.1 22
Engines p. 143

Find out move

express them. He explained how gravity keeps the planets
in orbit around the Sun. Newton was honoured by being
buried in Westminster Abbey in London, England.

hand is equal to the momentum
lost by the ball. The greater the
mass and velocity of an object,
the larger its momentum.

Jupiter p.290
Solar system p.283
Amphibians p.328

120

FORCES AND ENERGY

Friction

It IS HARD TO DRAG A HEAVYWEIGHT along a rough surface.

This is because there is a force called friction, which slows down the
movement of objects sliding over each other. Friction occurs because
no surface is perfectly smooth. This means that when any two surfaces
press together, the rough pieces, however tiny, catch on each other.

The rougher the surfaces, the more friction there is. If there were no
friction, it would be easy to drag large weights. But if there were no
friction, everything would keep sliding. You would not be able to walk
as your shoes would not grip the ground; you would not be able to
pick anything up because you would have no grip between your
fingers and the object. Friction

causes wear and tear which is ^

why even metal wears down. allows lhe air 10sIi p

past more easily.

AIR RESISTANCE
When an object moves
through air, the air
molecules bump against it
causing friction. This
friction is called air
resistance and it
becomes greater the
faster the object is
moving. Friction
makes things hot, so
when a meteor
hurtles through
the Earth’s
atmosphere it
becomes so
hot it begins
to break up.

The helmet is as
streamlined as possible.

Handlebars are covered with
rough material to increase
friction between them and the
hands for better

Brake pads press
against the rim of the
wheel and friction slows

Friction

EVERYWHERE

There are many places on
a bicycle where friction
acts. In some places,
such as between the
brake pads and the
wheels, it is
important to have
friction. In other
parts, such as
the gears, you want
as little friction
as possible.

STREAMLINING IN NATURE
Objects experience friction
moving through water too.
This is called drag. A bird
diving for a fish puts its wings
back to make a streamlined
shape. And most fish are
streamlined so they can move
through the water easily.

Tyres grip the road with friction.
They have a pattern of grooves
called the tread which allows
water to escape from under
the wheels. Otherwise,
any water on the road
would act as a lubricant
and reduce the friction
and the grip.

Oil flows into the
“valleys” in the rough
surfaces.

stop the cyclist’s feet
from slipping off.

and gears are
lubricated with oil to
reduce friction.

CHRISTOPHER COCKERELL

A British engineer, Christopher
Cockerell (born 1910) invented the
hovercraft in 1955. He thought up
the idea of using a strong downward
jet of air to push a boat up and away
from the water, letting it move without
friction. When Cockerell told the British
government of his invention, they were so impressed that
they placed the invention on the Top Secret list! He was
eventually given permission to manufacture the new boat.
The first large hovercraft was launched in 1969.

Air is drawn in and forced under the hovercraft.

A “skirt" of flexible material around the hull stops
air leaking out. The hovercraft rides on
this cushion of air which reduces
friction between it and the water.

drive the craft forwards.

REDUCING FRICTION
Friction can cause machine
parts to wear out, but it can be
reduced by using ball bearings
lubricated, or coated, with oil.

The ball bearings work because
they roll rather than drag
across each other.

Find out more

Acceleration p.119
Measuring forces p.123
Machines p.130
Engines p.143
Comets and meteors p.295

121

FORCES AND ENERGY

Centre of
gravity

Jumping on
the Earth

BOOMERANG

Some objects, such as a boomerang,
have their centre of gravity outside
their body. Because of its shape, a
boomerang cannot be balanced by
supporting it at one point on its flat
side. Edge-on, it will balance when
supported at the point of the V.

TIDES

Gravity causes the tides.

The ocean on the side of
the Earth nearest the
Moon is pulled outwards by
the Moon’s gravity, creating a
high tide. It is high tide on the
far side of the Earth at the same time
because the Earth is pulled towards the Moon more
than the water on that side. The Sun has a small effect
on tides. When Moon and Sun are in line, their gravity
combines to produce a high spring tide.

Gravity

When YOU DROP SOMETHING, it falls to the ground. The force
that makes it do this is the Earth’s gravity. Gravity is a force that pulls
objects together. It is not just the Earth that has gravity. The Moon has
gravity too. And the Sun’s gravity attracts the Earth and planets and
holds them in their orbits. The force of gravitational attraction
between two objects depends upon the distance between them - the
greater the distance, the smaller the force pulling them together.
It also depends upon the masses of the objects - the
greater the mass of the objects, the greater the
force of gravity.

Centre of gravity

The point at which the effect of gravity on an object
seems to be concentrated is called the centre of gravity. It
is the point where the whole weight of the object seems
to act. An object can be balanced if it is supported
directly in line with its centre of gravity. But balancing
is easiest if the object has a low centre of gravity.

1. Hang the object and the
plumbline together from the
same point. Draw a line
where the plumbline falls.

On the Moon

On Earth

Plumbline

FINDING THE CENTRE OF GRAVITY
It is easy to find the centre of gravity
of a flat object such as this kite.

Hang the object and a plumbline together so that they
can both .swing freely. When they are still, the centre of
gravity will be directly below the point of suspension
somewhere on the plumbline. Draw a line to show where
the plumbline falls. Repeat this from a different point
and the centre of gravity will be where the two lines cross.

2. Hang the object and
plumbline from another
point on the object and
again mark where the
plumbline falls.

MASS AND WEIGHT
Mass is not the same as weight. Mass is
the amount of material in an object;
weight is the force exerted on an object’s
mass by gravity. On the Moon, a pile of
strawberries would weigh one-sixth as
much as it does on Earth but the mass
would be the same. This is because the
Moon’s surface gravity is
one-sixth as strong as
the Earth’s.

Jumping on the Moon

This cork is
supported on the
point of a needle. It is
balancing because
the heavy forks
hanging underneath
have put the weight of
the whole object, and
the centre of gravity,
lower down, directly
under its support.

Centre of gravity

THE MOON’S GRAVITY
Gravity on the Moon is less than
that on the Earth because the
Moon is much smaller and has less
mass than the Earth. On the
Moon, falling objects accelerate
downwards at one-sixth the rate
they do on the Earth, and a person
can jump six times as high on the
Moon as on the Earth.

Find out more

Measuring forces p.123
Turning forces p. 124
ClRCUIAR MOTION P.125

Waves, tides, and currents
p.235

SoiAR SYSTEM P.283
Rockets p.299

122

FORCES AND ENERGY

The
weight
of this
apple is
slightly
less than
1 newton.

o —

_ i -

— 0

Kr.i

2 —

3 —

4 —

— 2

-3

— 4

5 —

C. _

-5

_ C

D —

7 —

G _

— 0

-7

_ Q

o —"

9 —

“ o

-9

10 —

— 10

11 —

— 11

12 —

- 12

13 —

— 13

14 —

— 14

15 —

— 15

16 —

-16

17 —

-17

18 —

-18

19 —

— 19

20 —

— 20

Measuring forces

The SIZE OF A FORCE is usually expressed
in units called newtons, named after Sir Isaac
Newton. On Earth, a mass of 1 kg (2.2 lb)
weighs almost 10 newtons - 9.8 newtons to be
exact. A spring balance is often used to
measure a force because springs are elastic -
they stretch. The inventor Robert Hooke
discovered that the amount an elastic body
stretches out of shape is in direct proportion
to the force acting on it. This is known as
Hooke’s law. As long as the force is not too
large, stretching the spring past its limit of
elasticity, the spring will go back to its original
length when the force is removed.

Cavendish
measured
how much the
beam moved
to calculate
the gravity
between the
balls.

i 0

The newtonmeter

It is helpful when imagining a newton to know
that 1 newton is about the force needed to lift a
small apple. Forces up to about 100 newtons can
be measured using a newtonmeter. As the
spring inside is stretched, a marker moves down
a scale along the side of the meter and indicates
the size of the stretching force - in this
case the weight of an apple.

MEASURING GRAVITY
Englishman Henry Cavendish (1731-1810)
used this apparatus to calculate the Earth’s
mass. He hung two lead balls from the
ends of a beam which turned horizontally.
The balls were attracted by gravity to two
larger lead balls nearby. As the small balls
moved, they turned the beam. Cavendish
calculated the gravity between the balls
and, from that, the mass of the Earth.

COMPARING FORCES
Lifting a ball requires a force of
about 4 newtons. A kick applies a
force of about 10 newtons to the ball.
Compare this with the
n force of a jet engine -
100,000 newtons. On a
small scale, an insect
\ jumping into the air
uses a force of about
0.001 newtons.

ROBERT HOOKE

English inventor
Robert Hooke
(1635-1702) is best
remembered for
discovering how
elastic objects
stretch. He was a skilled
instrument-maker and helped
improve scientific instruments such
as microscopes, telescopes, and
barometers. He designed a
telegraph system and a watch
regulated by a vibrating spring,
rather than a pendulum. In 1665,
he published a book containing
drawings of insects seen through
the microscope.

MEASURING FRICTION
You can measure the drag produced by friction
at home. Attach an iron mass to a block of
wood with string and hang it over the edge of
a table. See how much weight you need to
make the wood move along different
surfaces. Friction depends on the surfaces
rubbing together and the weight of the
sliding block. The area of the surfaces in
contact does not matter.

Find out more

Prof

•ERTIES OF MATTER

Friction p. 121
Gravity p.122
Vibrations p.126

p.22

123

FOKCES AND ENERGY

VEHICLE TESTING

Tall vehicles are made
safer by putting their
wheels wide apart and
their engines low down.
This keeps their centre
of gravity low. This bus
is being tested to see
how far it will tip before
it topples over.

Turning forces

When YOU TURN THE HANDLEBARS of your bicycle, you pull on
one side and push on the other. This pair of forces is an example of a
couple, or pair of turning forces. The point around which an object
turns is called the fulcrum, or pivot. A single force can
make an object turn if it acts some distance away from
a fixed fulcrum. When you open a door, you apply a
single force to the door handle and the door turns
as it swings open. The door hinge is the fulcrum
around which the door turns. The turning effect
of a force depends upon the size of the force
and how far away from the fulcrum the force
is acting. The further away the force, the
greater the turning effect.

More weight presses down
through the back wheel of a
bike than through the front wheel. For
the plank to balance, the back wheel of
bike must be closer to the log

than the front wheel. 'iM&B

MAXIMUM FORCE
In some countries, cattle are used to
turn a wheel to raise water. They arc
harnessed to the end of a pole attached
to the wheel. As they walk round, they
turn the wheel. It is easier for them if
the pole is as long as possible to make
their turning force greater.

Fulcrum

BALANCING THE FORCES
When an object is in equilibrium, or
balanced, the turning force on one
side of the fulcrum is equal to the
turning force on the other side. A
cyclist in trial riding uses this principle
when he stops a plank from seesawing
down over a log before he is ready.

Centre of

A tall bottle almost full
of water is unstable
because it has a high
centre of gravity. The
centre of gravity
does not stay above
the bottle’s base
when the bottle is
tipped, so
producing a
turning force
that topples it.

A bottle containing a
small amount of water is
stable as it has a low
centre of gravity. The
centre of gravity remains
above the base of the
bottle when it is tipped
slightly, producing a
turning force that
returns the bottle to its
original position.

Bar marked
scale

A steelyard used by
the Ancient Romans

Hook for item
to be weighed

Balancing

bob

WEIGHING SCALES
The Ancient Romans used turning
forces to weigh things on a
steelyard. Steelyards are still used
today. You may get weighed on a
steelyard at the doctor’s. While you
stand on the scales, a bob is moved
along a bar until the bar balances.
Your weight can then be read from
a scale on the bar where the
balancing weight stops.

Stability

An object is said to be in stable equilibrium if, when
pushed slightly, its centre of gravity is still lying above
its base. Gravity pulls the object back to its original
position. If an object falls over when pushed slightly,
it is in unstable equilibrium. Its centre of gravity is
no longer above its base and gravity pulls the object
further. An object is in neutral equilibrium if it
remains in its new position when pushed slightly.

Centre of

Find out more

For

Mf.,

CF.S AND MOTION P

Gravity p.122

\SURING FORCES P.

Machines p.130

.120

123

124

FORCES AND ENERGY

J Find out more

Forces and motion p.120
Friction p. 121
Gravity p. 122
Rockets p.299

WEIGHTLESSNESS IN ORBIT

A space shuttle is held in orbit
around the Earth because the
Earth’s gravity provides a
centripetal force, which makes it
move in a circle rather than fly
off into space. Astronauts inside
the shuttle are affected by
gravity to the same extent. They
feel weightless because they are
continuously falling. But they are
moving forwards at such a speed
that they are carried “over the
horizon” in a circular path that
never gets any nearer the ground.

Circular motion

The faster the thrower
spins, the further the
hammer will fly when
he lets go.

Wheels, SPINNING TOPS, propellers, and
roundabouts all go round in circles. They are
really changing direction all the time. Each part
of the spinning object is trying to move forwards
in a straight line, but a force is pulling them in
towards the centre of the circle. This force is
called centripetal force. It continually changes
the direction of a turning object so that it goes
round in a circle and not in a straight line.

When an animal, running at speed, makes a
tight turn, its feet push into the ground. The
ground pushes back and this provides a
centripetal force. If the animal was running on
ice and could not grip the ground, there would
be no centripetal force and the animal would
find it extremely difficult to make the turn!

SPINNING GYROSCOPE
Spinning objects have inertia, just
as objects moving in a straight line
have. They resist having their
direction of movement changed. A
gyroscope is a device that contains a
spinning wheel. If the wheel is
spinning fast enough, it resists
gravity and it is then very difficult to
push the gyroscope over.

Electrically driven gyroscopes are
used in navigation systems on
aeroplanes and ships.

The water is level when
the bowl is not spinning.

HAMMER THROW
A hammer thrower spins the
hammer round as fast as he can
before releasing it. The centripetal
force needed to keep it spinning
round is the pull on the wire. When
the thrower lets go of the hammer,
he removes the centripetal force
and the hammer’s inertia makes it
fly off in a straight line.

As the bowl
spins, the water
rises up the

CLIMBING WATER
If a bowl of water is spun quickly
round and round, the water tries
to fly out in a straight line. A
force is needed to stop it. This is
provided by the walls of the bowl.

The faster the bowl spins, the
more the water moves outwards.

A spin dryer uses this effect to remove
water from clothes. The water moves towards the walls of
the drum, and if it finds one of the holes it flies straight through.

Turntable spinning
the bowl round.

CENTRIFUGAL FORCE
A toy car racing round a loop-the-
loop track does not fall off, even
when it is upside-down. A force
appears to be pushing it upwards.
This is sometimes called
centrifugal force. But centrifugal
force is really inertia trying to
make the car go straight on.

125

FORCES AND ENERGY

PIEZOELECTRICITY

Quartz has a special property - an
electric charge changes its size.

Because of this piezoelectric effect, a
suitable electric current makes a
crystal vibrate at a precise frequency.

In a quartz watch, current from a
battery makes a micro-thin slice of
quartz crystal vibrate 32,768 times
each second. A microchip reduces
this rate to produce a signal once a
second. This signal controls the motor
that turns the hands or activates the digital display.

The size of the
movement or
vibration is
called the
amplitude.

The time
taken for one
vibration is
called the
period.

Vibrations

If YOU HANG A MASS from a piece of string, and
push the mass to one side, it will swing from side to
side in a regular way. These back and forth movements
are called oscillations, or vibrations. The number of
times an object vibrates in one second is called the
frequency. Everything has a natural frequency. If you
force an object to vibrate at its natural frequency,
the oscillations get larger. In 1940, the wind made
the Tacoma Narrows bridge in Washington State,
United States, vibrate at a rate that matched its
natural frequency. The vibrations became so
violent that the bridge collapsed. But vibrations
can also be useful. Pneumatic drills use
vibrations to break up materials,
and clocks measure time by
counting regular vibrations.

Crest

SOUND WAVES
When a musical instrument
such as the cymbals vibrate,
they cause sound waves in the
air. In a sound wave, air
particles vibrate back and forth
in the same direction as the
wave is travelling. They are
longitudinal waves.

WATER WAVES
Ripples on a pond or
waves on the sea are
transverse waves. As
the wave passes, water
particles vibrate up
and down at right
angles to the
direction of the wave.

PENDULUM

The swing of a pendulum is a vibration. The
time taken for one swing depends only upon the
length of the pendulum, provided the swings are
small. The weight of the bob on the end does
not matter. Italian experimenter Galileo
suggested that a clock could be regulated by a
pendulum. In a pendulum clock, the pendulum
swings and turns a wheel at a regular rate. The
wheel turns the hands of the clock.

Waves

Vibrations cause waves. Some waves are obvious, as
on the sea and on the surface of a pond. But some
waves are not so easy to see, for example sound
waves, which are caused by something vibrating.
Waves can be transverse or longitudinal.

EARTHQUAKE VIBRATIONS
Vibrations caused by an
earthquake can make buildings
collapse. This special effects photo
symbolizes an earthquake in San
Francisco, United States. San
Francisco lies on the San Andreas
fault, one of the world’s great fault
lines. A fault line is where
earthquakes are likely to happen.

Find out more

Crystals p.30
Sound p.178

ASURING SOUND P.
ARTHQUAKES P.22(
Waves, tides, and
CURRENTS P.235

180

126

FORCES AND ENERGY

Pressure

Why do camels have large, flat feet? Why

does a pin have a sharp point? The reason is
because if you spread a force over a large area,
the pressure of the force will be reduced. And
by concentrating a force into a small area the
pressure will be greater. A camel does not sink
into the sand because its weight is spread over
a large area. But when you push a drawing pin
into a notice board, the sharp point goes into
the board easily because the force of your
thumb is concentrated into a tiny area.

Pressure is measured by
the force acting on a
single unit of area.

SPREADING
THE LOAD
The jacana bird
of South America
has exceedingly long
toes and claws. Its weight is
therefore spread over a large area and it can walk
on the floating lily pads without sinking.

At sea level, air
pressure is roughly
equal to the weight
of a cow sitting on a
large dinner plate.

People cannot dive
deeper than about
120 m (400 ft) as the
water pressure would
crush them.

20,000 m (66,000 ft) high

Air pressure at
20,000 m (66,000 ft)
is less than one-tenth
that at sea level.

On mountain tops,
the air is thin so
climbers usually
use breathing
apparatus to give
them more oxygen.
Air pressure is half
that at sea level.

SINKING IN
A watering can does
not sink into soil because
its weight is spread over its
base. But a trowel is easy to
push into soil as its
weight is concentrated
into the thin edge. A
sharp knife cuts easily
for the same reason:
the force on the knife is
concentrated into a
small area along the
cutting edge.

EVANGELISTA
TORRICELLI

Air pressure is measured
with a barometer. The mercury
barometer was invented by
Italian Evangelista Torricelli
(1608-47) in 1643. He
discovered that the height of mercury in a
tube placed upside-down in a cup of mercury
varies as air pressure changes. Torricelli learnt
from Galileo and eventually succeeded him as
court mathematician to the Grand Duke of
Tuscany. A unit of pressure, the torr, is named
after him. One torr is the pressure that
supports 1mm (0.04 in) of mercury in a

barometer.

Airliners fly at a
height where air
pressure is less
than pressure inside
the body. It would be
impossible for the
body to take in air, so
the inside of airliners
is pressurized.

Submarines can dive
deep under water.
They have thick hulls
to withstand the
great water pressure.

Water squirts furthest
through the lowest
hole because
pressure increases
with depth.

PRESSURE IN LIQUIDS
The pressure in liquids acts in all
directions. The water squirts through
the holes in the side of this container
because of horizontal pressure.

UNDER PRESSURE

Liquids and gases, both called fluids, exert pressure on objects.
Air exerts pressure on you. If it were not for the fact that the
fluids inside your body exert as much pressure as the air outside,
the pressure of air at ground level would crush you! Air pressure
decreases the higher up you go as there is less and less air.

10,000 m (33,000 ft) deep

At a depth of
10,000 m (33,000 ft)
under the ocean,
the pressure of
water is equivalent
to seven elephants
balanced on a small
dinner plate!

Find out more

Bee

[AVIOUR OF GASES ]
►RCES IN FLUIDS P.l

Atmosphere p.248
\IR PRESSURE P.25C

p.51

127

FORCES AND ENERGY

FORCES in FLUIDS

fM SURFACE
m TENSION
f A liquid behaves as if
its surface was covered by
an invisible stretched skin.

Meniscus curves

LIQUIDS AND GASES both flow when a force acts on
them. They are known as fluids. Fluids have no definite
shape and take the shape of their container. When
fluids are squeezed by a force, the force
is transmitted to all other parts of
the fluid. This is called Pascal’s
Principle and it is used to drive
some machinery. In the
hydraulic brake of a car, for
example, the force applied to the brake
pedal is transmitted to the wheels by a
liquid, called the brake fluid. Another
useful property of fluids is that a fast-
moving fluid has a lower pressure
than a slow-moving one. This is
known as Bernoulli’s Principle. It
enables lumbering aeroplanes to
soar high into the sky.

A bird’s
wing is shaped
like an aerofoil,
giving it lift.

The extra pressure
underneath pushes
the wing upwards.

BIRD WINGS
A bird gets most of
its lift by flapping its
wings which push the
air downwards
producing an upward
reaction force. However,
when the bird is just gliding,
the wing itself produces some
lift because of its shape.

AEROFOIL

The wing of an aeroplane is curved
on top and nearly flat underneath.
This special shape is called an
aerofoil; it rises when air, which is a
fluid, flows around it. This is
because air flowing over the top of
an aerofoil-shaped wing travels
faster than air passing underneath.
According to Bernoulli’s Principle,
this means that the pressure under
the wing is greater than the
pressure over the wing, creating lift.
The faster the air flow, the greater
the lift. This is why an aircraft must
be travelling very fast to take off.

bubbles can be
stretched into strange shapes
because soap weakens the
surface tension of water.

This effect is called surface
tension. It is caused by
forces between molecules
pulling those molecules at
the surface inwards. A
bubble is normally a sphere
because surface tension
pulls it into this shape.

of water
creep up
the sides
of the
tube.

CAPILLARY ACTION
If a liquid is at the bottom
of a very narrow tube, it
may move up the tube.

This is known as
capillary action. It will
happen if the force of
attraction between
the liquid molecules
and the molecules of
the tube is stronger
than the attraction
between the liquid
molecules themselves.

BLAISE PASCAL

Frenchman Blaise
Pascal (1623-62)
was a brilliant
mathematician and
religious thinker. He
made the first successful
calculating machine at the age of
22. In 1646, he made a mercury
barometer and later used it to
measure air pressure. While
studying liquids, he discovered the
principle named after him. Pascal’s
Principle states that, in a liquid or
gas, pressure applied to one point is
transmitted equally to all parts of
the fluid. Pascal’s name is given to a
unit of pressure. One pascal (Pa) is
1 newton per square metre.

Mercury

COHESION AND ADHESION
The surface, or meniscus, of water in a
tube is curved upwards but that of
mercuiy is curved downwards. This is
because the particles of mercury are
strongly attracted to each other; they
have strong cohesion (and a high
surface tension). Cohesion is a force
between particles of the same type.
The water particles are more attracted
to the glass particles of the tube. This
force between two different materials
is called adhesion. It is the reason why
raindrops stick to a windowpane.

curves
-upwards.

Water

Find out more

Properties of matter p.22
Bonding p.28

Soaps and detergents p.95
Adhesives p.106
Pressure p.127
Calculators p.172
Air pressure p.250
Fact finder p.408

128

FORCES AM) ENERGY

Floating and sinking

ARCHIMEDES

It is said that
Archimedes, a
Greek inventor
who lived in the
third century B.C.,
discovered his
Principle after
noticing that his bath
overflowed when he got
into it. He ran through the streets
naked, shouting “Eureka!” (“I’ve
got it!”). With his principle, he
helped to prove that the King’s
goldsmith had tried to cheat him
by putting silver into a gold crown.
Archimedes made discoveries in
hydrostatics (science of stationary
fluids), geometry, and mechanics
(science of machines).

GOING UP
Helium
balloons rise
in air because
helium is less
dense than
air. The
weight of air
the balloons
displace is
greater
than their
weight.

Why DOES AN OBJECT seem to get
lighter as you lower it into water? It is
because the water pushes against it,
supporting some of its weight. This
supporting force is called the upthrust.
Upthrust is equal to the weight of fluid
an object displaces, or pushes away. This is
Archimedes’ Principle. An object will float
if the upthrust is equal to its weight. It will
sink if its weight is greater than the upthrust.
Whether something floats, depends on its
density - a measure of how packed together its
matter is. A wax candle floats on water because it
has a low density and displaces enough water to
provide a large upthrust. A stone is denser than water
and sinks: the displaced water does not equal its weight.
The stone pushes away with more force than that of the
water pushing up.

SUBMARINES

Inside a submarine there

are containers called ballast tanks.

If these are full of air, the submarine will
float. Even though it is made of steel, the
average density of the submarine is less than
that of water. By pumping water into the
ballast tanks, the submarine can
sink. This is because with its
ballast tanks full of water, the
submarine has a higher
density than water.

FLOATING IN WATER
A peach floats in water because the
weight of water it displaces is equal to its
own weight. This means that the force
of the upthrust exactly equals the force
of the peach’s weight pushing down.

Propellers drive the
forwards.

When a submarine is on the
surface, its ballast tanks are full of
air which keeps it afloat.

To dive, water is
pumped into the ballast
tanks, making the
submarine heavier.

To rise, air is pumped into
the ballast tanks, making
the submarine lighter.

Swim bladder

FISH

Some fish have a swim bladder like
the ballast tanks of a submarine.
Air can enter this bladder either
via the fish’s mouth, or from the
bloodstream. This enables the fish
to rise in the water.

Cork-
Oil —

Plastic

block

Water

Grape

Syrup

HIGHER OR LOWER?
Oil floats on water because it is
less dense than water. Water
floats on syrup because it is less
dense than syrup. A cork is less
dense than all three liquids,
and so floats on the surface of
the oil. A plastic block has a
density lower than water but
higher than oil. This means it
sinks through the oil, but floats
on the water. A grape has a
higher density than oil or
water, but lower than syrup. So
the grape floats on the syrup.

Find out more

Prof

’ERTIES OF MATTER

>RCES IN FLUIDS P.l

Machines p.130
Fish p.326
Fact finder p.408

. p.22

FORCES AND ENERGY

MACHINES

INSIDE A PIANO

A pianist needs to play notes quickly to
produce good music. Each key in a piano is
linked to a complex system of levers that
magnify movement. The pianist has to use only
a small finger movement to make the hammer
hit the piano wire strongly, and sound a note.

Damper to cut
off the sound

Piano wire

Felt-tipped

hammer P'anokey.

Not all machines are large and noisy.

Many are small and they are used to do
simple jobs. But whatever their size, all
machines make a particular job easier to
do. Some machines can change a small
movement into a large one;
some can change a small force
into a large one; others can
change the direction or
position of a force, and apply
it where it is most needed.

The smaller the effort force,
the greater distance it must
move. This is called the
Principle of the Machine.

Unfortunately all machines are
less than 100 per cent efficient.

Some of the effort put in is not
used to do the job in hand, but to
overcome friction between parts.

Threshing cylinder
separates the grain
from the heads.

Grain auger
carries grain to
grain tank.

MAGNIFYING
MOVEMENT
When a rowing
eight use their
oars to move the
boat, they are using
machines that
magnify' movement.
They move the inner
end of the oars a
small distance but
the other end of the
oars moves a larger
distance, pulling the
boat swiftly through
the water.

ROUND AND ROUND
It is easier to walk up a mountain
by taking the winding road than
to try to walk straight up the side.
The winding road is acting as a
simple machine. It decreases the
effort you use to reach the top of
the mountain, but increases the
distance you must move.

Complex machines

A combine harvester is a complex
machine, but it is made up of lots of
simple machines connected together
in many ingenious ways: by gear
trains, levers, moving belts, and
hydraulic pipe systems. The result is a
useful tool that
combines the two
parts of harvesting -
cutting the crop and
separating the grain
- hence its name.

Auger unloads
the grain.

Conveyor carries the
stalks up to the
threshing cylinder.

Auger carries
corn to conveyor.

Reel feeds
corn to
cutting bar.

Cutter bar
slices the
stalks.

MAGNIFYING FORCE

Archimedes, the Ancient Greek inventor,

said, “Give me a lever long enough, and I

could move the world”. In
theory, this statement is true
because a lever magnifies
force. For example, a
claw-hammer, a type of
lever, can be used to
remove a nail from a
piece of wood.

If you pull gently down on
the handle of the
hammer, the claw at the
other end will exert a
large force on the nail.

130

FORCES AND ENERGY

Simple machines

Slopes, wedges, screws, levers, wheels and axles,
pulleys, and gears are all called simple machines.
They can make a job easier to do because they
allow a small force, the effort, to overcome a
larger force, the load. Machines that increase
force are said to give a mechanical advantage.
Mechanical advantage can be calculated by
dividing the load by the effort. In machines
that are used to increase movement,
the advantage, called the velocity jg||

ratio, is calculated by dividing the
distance the load moves by the
distance the effort moves.

WEDGE

The blade of an axe is a
wedge - a machine that
magnifies force. When
the axe is swung into the
wood, the force of the
swing is transferred to the
blade. The blade moves
forwards through the
wood, and forces it to
split apart. The wood
moves a smaller distance
than the blade but with
more force.

Effort

There are four strands
of rope pulling up on the
lower pulley and the
load. This multiplies by
four the load that can be
lifted with a given effort.

Xoad

PULLEY

A pulley is useful for lifting things up vertically.

It is simply a piece of rope wound round a wheel.
One end of the rope is attached to the load, and
force is applied at the other end to lift the load.
A pulley magnifies force when more than one
wheel is used. One wheel is attached to the load
and the others to a support, such as a beam.

GEARS,

AND WHEEL AND AXLE

A rotary egg whisk contains two
kinds of machine: gears, and
wheels and axles. Gears are toothed
wheels that are interlocked in pairs.
They can magnify speed or force.
Usually, one wheel is larger than
the other. A wheel and axle
magnifies force because the wheel
is larger than the axle. The axle
turns in a smaller circle but with
greater force.

The handle turns a wheel,
which itself turns a
smaller wheel at

The axle __ greater speed,
transmits the
turning motion
to the
blades,
which
rotate at
high speed.

Load

Fi ilrn im

Load

Fulcrum

Load

LEVER

A lever is a rod or bar that turns about a point called
the fulcrum, or pivot, to move a load. There are three
kinds of lever, with different arrangements of load,
effort, and fulcrum. Some levers magnify force, others
magnify movement. For a lever to be a force magnifier,
the effort must be applied further away from the
fulcrum than the load. There are examples of levers in
your body. For example, your arm is a class three lever.
Your elbow is the fulcrum, the muscles in your arm
provide the effort, and your hand is the load.

Pliers are a class 1 lever - a
force magnifier.

Nutcrackers are a class 2
lever - a force magnifier.

INCLINED PLANE

It is easier to push something up a slope, or
inclined plane, than to lift it straight up. Removers
use a ramp to load heavy items into a van. They
have to move things further than they would if
they lifted them vertically, but they need to use
less effort. An inclined plane
is therefore
^ a force

magnifier.

Tongs are a class 3 lever - a
distance magnifier.

The thread of a
screw is like a
slope wrapped
round a cylinder.

Handle is turned to
turn the screw.

Wooden tube cut
away to show
the screw.

Archimedes

screw

SCREW

The thread of a screw is really an?inclined plane. A
screw can produce a mechanical advantage because it
turns around a greater distance than it moves forwards.
This means that it moves forwards with a greater force
than is used to turn it. Water is sometimes lifted, for
example from a river to irrigate a field, with a device
called an Archimedes’ screw. Each time the screw
turns, it lifts water a little bit higher up inside a tube.

Find out more

Forces and motion p.120
Turning forces p.124
Floating and sinking p.129
Musical sounds p.186
Skeletons p.352
Fact under p.408

131

FORCES AND ENERGY

When an apple
that weighs
1 newton is
lifted vertically
by 1 m (3.3 ft),
a joule of work
is done.

WORK AND ENERGY

To A SCIENTIST, work is done only when a force
moves something. If you lift a heavy object, you do
work because you exert a force which moves that
object. Work cannot be done without energy. Energy
is the ability to do work. When work is done, energy
is used, or converted from one form to another. You
get your energy from your food; it is called chemical
energy. Some machines get their energy in chemical
form - from fuels such as petrol or gas. And there are
other forms of energy: heat, light, sound, nuclear,
and electrical energy. To understand how and why
things move we need to know what kind of energy
they have, and how much.

MEASURING WORK
When a fork-lift truck lifts crates, it
is working to overcome the force
of gravity. The heavier the crates,
and the further the truck lifts
them, the more work is done.

JOULES
The joule is used as the unit for
work as well as energy. One joule
is the work done when a force of
1 newton moves something a
distance of 1 m (3.3 ft) in the
direction of the force.

NATURAL ENERGY
A dung beetle uses energy stored
in its muscles to do work - in
this case, to push a ball of dung
up a slope. The heavier the ball
is, and the higher it is pushed,
the more work the beetle
does, and the more
energy it uses.

FOOD ENERGY

You would not be able to stay alive
without the energy you get from
food. But it can be just as bad for
you to take in too much energy as
too little. Different kinds of food
contain different amounts of
energy. For example, you would
have to eat about 1 kg (2.2 lb)
fresh tomatoes to get as much
energy as you would from just
24 g (0.8 oz) milk chocolate.

JAMES JOULE

Englishman James
Joule (1818-89)
was one of the first
to realize that
work produces
heat and that heat
is a form of energy.
He rotated paddles in
a container of water and
the water became warmer.

The more work that was done to
turn the paddles, the hotter the
water became. Joule realized that
work was changing movement
energy into heat energy. Joule
loved experimenting. He once
found that the water at the base of
a waterfall was hotter than the
water at the top, proving that the
energy of the falling water was
being converted into heat.

ENERGY REQUIREMENTS

Energy is measured in units called joules, but the joule is a small unit. There
are 1,000joules in a kilojoule (kj) - a unit used for measuring the amount of
energy in our food. Kilocalories (kcal) are also used. One kilocalorie is equal
to 4.2 kilojoules. Males and females, babies, teenagers, and adults, all use
different amounts of energy every day, and it
depends on what they are doing. A teei
boy needs about 12,600 kj (3,000 kcal)
energy each day. A teenage girl needs
about 10,500 kj (2,500 kcal).

Baby - 4,620 kJ
(1,100 kcal)

8,400 kJ Girl- 10,500 kJ
(2,000 kcal) (2,500 kcal)

12,600 kJ Woman - 9,200 kJ
(3,000 kcal) (2,200 kcal)

Man -
12,600 kj
(3,000 kcal)

Man doing
manual work-
16,800 kJ
(4,000 kcal)

132

FORCES AJND ENERGY

Types of energy

A moving object has energy, called kinetic
energy. The energy of a moving car could
demolish a brick wall. Where there are
forces, there is also stored energy, called
potential energy because it has the potential
to turn into kinetic energy. Chemical energy
is a form of stored energy. It is stored in
the chemical make-up of some
substances such as plants, oil, yJmmjy

coal, and batteries.The most
versatile form of energy is JjgKw

electricity. It can be easily
converted into other MW/m

forms of energy: ■

light, sound, flL

and heat.

JAMES WATT

\ Scottish engineer

James Watt (1736-
1819) became
Mathematical
H Instrument Maker at

the University of
Glasgow when he was
20. While repairing a
model steam engine, he
realized how the engine could be
improved by having two cylinders.
He made a full-scale improved
engine which was much more
powerful and economical than
earlier engines. His engines were
soon used in factories and mines all
over the country and were exported
to Europe and North America.

A portable television
has chemical energy
stored in its battery.
This is released when
an electric current
flows through the
television to produce
heat, light, and sound.

It takes two children to
lift the weight as
quickly as the man.

A kitten has chemical
energy stored in its
muscles. It uses

some of this lH|

energy to climb up ^j|
a tree. As it climbs,
it increases its

gravitational potential energy - the
potential to fall off! When it falls,
the kitten will have kinetic energy.

POWERLIFTING
Power is the rate at which
work is done, or how quickly '
one form of energy is changed
to another. A man is more
powerful than a child. He can lift
a load quickly, but children can
only lift it slowly. The unit of
power is the watt which equals
1 joule per second. /

A plant has chemical
energy stored in its J

leaves. This can be
released if the chemical
make-up of the plant is
changed, for example if it is
eaten by an animal or burnt to
produce heat and light.

POTENTIAL ENERGY
Potential energy is the energy that a body has
because of its position or because of the state it is
in. For example, a jack-in-the-box has potential
energy when it is squashed into its box. Types
of potential energy are: gravitational
HPB potential energy (of a raised object),

elastic potential energy (of a stretched or
squashed elastic material), electrical
potential energy (of an object near an
electric charge), and magnetic potential
/ energy (of a piece of iron near a magnet).

A jack-in-the-box has
elastic potential energy
when it is squeezed
into its box.

KINETIC ENERGY

Windmills were originally used to drive
a machine such as a millstone. When
the sails turned, they moved the
millstone converting the kinetic energy
of the wind into the movement of the
millstone. The amount of kinetic
energy that a moving object has
increases with the mass and speed of
the object. If the mass of a moving
object is doubled, its kinetic energy is
doubled. If the speed doubles, the
kinetic energy increases four times.

Find out more

Energy sources p.134
Heat p.140
Engines p.143
Electricity supply p.160
Sound and light p.177
Factfinder p.408

. ^ When the lid of
the box is lifted, the
jack-in-the-box has kinetic
energy as it jumps up.

133

FORCES AND ENERGY

Silicon
doped (made
impure) with
phosphorus
which
produces
free

electrons.

Silicon doped with
boron, which
makes “holes"
where electrons
are missing.

Energy sources

phot^oitaic The AMOUNT OF ENERGY that the Earth gets

from the Sun is huge. Sunshine falling on the roads in
the United States in one year contains twice as much
energy as all the coal and oil used in a year

worldwide. The Sun’s energy shows in different
ways - as wind and waves, for example, as well
as direct solar energy. The only
forms of energy that do not come
originally from the Sun are nuclear
energy, the chemical energy in electric
batteries, tidal energy, and geothermal
energy. Some energy sources are known
as renewable energy since they will not
run out. Other energy sources, such
.X as oil and coal, are non-renewable -
they will run out eventually.

When sunlight falls
on the cell, electrons
are driven from one layer
to the other creating an
electric current. -—

SUNLIGHT INTO ENERGY

BIOMASS ENERGY

Energy derived from plants,
such as burning wood, is called
biomass energy. Almost half the
world’s population uses some
form of biomass energy for
cooking, heating, and lighting.
This man in India is using
biogas f or cooking. This gas is a
mixture of methane and carbon
dioxide produced from rotting
waste or animal droppings.

Electricity

generator

A wind turbine usually has a propeller-
type rotor mounted on a tall tower.

WIND POWER

Windmills have been used
to grind corn and pump
water since ancient times.

Today, wind turbines are
designed to generate
electricity. A wind
farm at San Gorgonia Pass in
California has 4,000 windmills
supplying electricity to the nearby
Coachella Valley. The world’s
largest wind generator is in Hawaii.
The windmill has two 50 m- (164 ft-)
long blades on top of a tower,

20 storeys high.

HOT ROCKS
Some rocks in the Earth’s crust
are as hot as 1,000 °C
(1,800 °F), making the
Earth a vast storehouse of
heat energy, called
geothermal energy. Some
of this energy makes its way
naturally to the surface as
hot water springs or steam
geysers. Sometimes water has
to be pumped down into the
Earth to be heated and then
returned to the surface. About 20 countries use geothermal
energy for heating or for generating electricity.

The Sun is an important non-polluting and
renewable energy source. The Sun’s energy can
be converted into electricity inside photovoltaic
(solar) cells. Photovoltaic cells are found in
solar-powered calculators, radio beacons and
telephone links in remote areas, space
satellites, and navigation buoys on the oceans.

Water from
a reservoir
falls
down to

A road runs along
the top to allow
traffic to cross
the estuary.

TIDAL POWER

The world’s first large tidal power station was built across the estuary
at La Ranee in Brittany, France. It can produce 240 million watts of
power - enough for a city of 300,000 people. As the tide falls, water is
kept at high tide level inside the barrage. When the difference in
water levels is about 3 m (10 ft), water is allowed to flow out of the
barrage to the sea, flowing through 24 huge turbines which drive
electricity generators. As the tide rises again, water is allowed to flow

through the barrage to
fill the estuary, until it is
high tide and the process
begins again.

WATER POWER
About one-fifth of the
world’s energy comes from
hydroelectricity. In a
hydroelectric power station,
the energy of falling water is
used to drive a turbine,
which in turn drives an
electricity generator.
Hydroelectric schemes can
generate large amounts of
power. The Itaipu scheme
on the Parana river on the
border of Brazil and Paraguay
has a potential output of
13,000 million watts.

Turbine

134

FORCES AM) ENERGY

Find out more

Nuclear energy p.136
Engines p.143
Cells and batteries p.150
Electricity supply p.160
Met amorphic rocks p.224
Waves, tides, and
CURRENTS P.235
Atmosphere p.248
Cycles in the biosphere p.372
People and planet p.374
Factfinder p.408

ENERGY IN THE HOME

In one year, an average house
uses five times the energy
used by all the runners in
the London or Boston
marathon. The main
source of energy in homes
is electricity, but coal, oil,
gas, and wood are also
used. A modern home
may heat water with a solar
heater - a glass-fronted box
with black-painted pipes
inside. Black absorbs the Sun’s
heat so that water flowing
through the pipes is heated up.

Electricity

generator

1859 First oil well drilled in
Pennsylvania, United States.

1880 First electricity generating
station built in London, England

1891 First hydroelectric power
demonstrated, in Germany.

1951 First nuclear electricity’
generated, in United States.

1960 First solar thermal power
plant built, in Turkmenistan,
former Soviet Union.

1968 First tidal power station
opened in France.

Cooling

tower

ENERGY SOURCES

c. 100 Romans use coal as fuel,
c. 650 Windmills in use in Persia.

Gas reserves
will last for
about 60 years.

Some heat
escapes
through the
chimney.

Inside a power station

A coal- or oil-fired power station contains a furnace
where the fuel is burned to heat water and make
steam. The steam drives a turbine attached to an
electricity generator. The electricity is sent to homes,
offices, and factories through a network of cables

called a grid. The steam is usually
sent through three turbines in
turn, until all its energy is
extracted. The steam is
turned back to
water in the
condenser.

Oil reserves will
last for about
40 years.

Condenser

Coal reserves
will last for about
years.

Transformer changes the
voltage before it is supplied
to homes and factories.

FOSSIL FUELS

Coal, natural gas, and oil are called
fossil fuels because they are the
remains of long-dead plants and
animals. They are convenient, power-
packed fuels, but when they are
burned, they release carbon dioxide
into the atmosphere, contributing to
global warming. They are also limited
and are being used up quickly. At the
present rate of consumption, the
world’s total reserves of fossil fuels will
run out in about 250 years.

Coal is crushed in a
mill and the powder is
blown to the furnace
where it is burned.

sprayed into the air to cool it.

FORCES AND ENERGY

Neutron

Fission

Normally, nothing can
penetrate an atom’s nucleus
because it is surrounded by
circling electrons. But a high¬
speed neutron can blast
through to be absorbed by
the nucleus. If the nucleus is
unstable, it will split into two
parts. This is nuclear fission.
Two or three neutrons are

Nuclear energy

The ATOM contains a huge amount of
energy - nuclear energy. This is due to the
strong forces that exist between particles in
the nucleus of an atom. Nuclear reactions
happen naturally: they power the Sun.
Humans have tried to harness nuclear
energy, but have only managed to obtain it
from certain atoms, such as those of
uranium, plutonium, and deuterium (a type
of hydrogen). One kilogram (2.2 lb) of
deuterium can produce as much energy as
three million kilograms (6.6 million lb) of
coal. There are two basic processes for
releasing nuclear energy: nuclear fission,
when the nucleus of an atom splits, and
nuclear fusion, when the nuclei of two or
more atoms fuse, or join together.

Energy
expelled

Neutron

RADIATION

These workers are preparing to
replace a fuel rod in the reactor core.
The core is under 10.5 m (35 ft) of
water to protect the workers from
the radiation produced. The blue
glow is due to the fact that energetic
charged particles travel faster
through water than light.

The heated fluid
is used to
produce steam.

The steam is piped to
turbines which are
linked to electricity
generators.

MASS INTO ENERGY

When a nuclear reaction
occurs, the mass of the
products is less than the
starting mass. Some mass
has vanished. Albert
Einstein showed that this
disappearing mass is
converted to energy. When a
mass, m, disappears, energy, E, is
released. E=mc 2 , where cis the speed of light. As cis a very
large number, a tiny loss of mass produces a huge amount
of energy. Just 1 kg (2.2 lb) of matter could produce as
much energy as a major earthquake, which can cause great
damage, as shown here in Mexico City in 1985.

NUCLEAR WASTE

Up to 97 per cent of the fuel in a nuclear reactor
can be recycled into fresh fuel and re-used.

However, the remaining 3 per cent is highly
radioactive and therefore dangerous.

Nuclear waste remains radioactive
even af ter 25,000 years, so must
be disposed of carefully. It can
be stored as a concentrated
liquid in stainless-steel tanks
that are surrounded in

concrete. The most
dangerous nuclear
waste can be turned
into glass blocks and
stored in deep
underground mines.

produced, which can go on
to blast more nuclei, setting
up a chain reaction.

Pellet of
uranium or
uranium
dioxide.

Fuel rods are
made of several
pellets.

The fuel rods are
embedded in a
material known as a
moderator, which
slows down the
neutrons produced.

The core is
surrounded by a
thick concrete
shield to absorb
radiation.

NUCLEAR
REACTOR

A nuclear reactor has a
core containing rods of uranium
(fuel rods). Among these are
boron rods (control rods) which
can absorb neutrons and control
the rate of reaction. As nuclear
fission occurs, heat is produced
which is used to convert water into
steam. The steam is used to
generate electricity.

In the reactor
core, there are
about 90,000
fuel rods.

A fluid circulates
through the reactor
core to carry away the
heat produced by
nuclear fission.

136

FORCES AND ENERGY

NUCLEAR WEAPONS

An atomic bomb uses uncontrolled
nuclear fission. If a certain
amount of uranium-235 or
plutonium-239 is brought
together, it will explode. A
hydrogen bomb uses nuclear
fusion. It is an atomic bomb
surrounded by deuterium.

When the atomic bomb
explodes, the high temperature
produced makes the deuterium
nuclei fuse. This photo shows
the city of Hiroshima in Japan
after an atomic bomb was dropped
on it in 1945.

Heavy hydrogen

(Deuterium)

nucleus

Neutron

expelled

Helium

nucleus formed

Energy
given off

HARNESSING FUSION
As yel, fusion is not a practical way to obtain
energy on Earth. Most fusion research uses
a machine called a tokamak. This holds
a doughnut-shaped vessel containing
the gas to be fused, called a plasma.

The plasma must be heated to a
temperature of millions of degrees
before fusion occurs. No container
could cope with such heat, so magnetic
fields are used to keep the hot plasma
away f rom the vessel walls.

NUCLEAR ENERGY

1905 German physicist Albert
Einstein shows that mass can be
converted into energy.

1919 New Zealander Ernest
Rutherford changes the nucleus
of a nitrogen atom into an
oxygen nucleus.

1939 German scientists Otto
Hahn and Fritz Strassman
announce the discovery of
nuclear fission.

1942 First nuclear reactor built
by Italian Enrico Fermi in a
squash court at the University of
Chicago, United States.

1951 First nuclear electricity
made by an experimental
breeder reactor at Idaho,

United States.

1956 The first commercial
nuclear power station starts up at
Calder Hall, England.

1986 An explosion in a reactor
at Chernobyl, Russia, releases
clouds of radioactive material,
which spread as far as Sweden.

1991 First controlled nuclear
fusion in JET (Joint European
Torus), at Oxford, England.

The circular
vessel containing
the plasma to be
fused is called
torus.

Heavy

hydrogen

(Tritium)

nucleus

Fusion

All the stars,
including the
Sun, gain their
energy from
nuclear fusion.
This is when two or more nuclei
stick, or fuse together. In the
Sun, for example, hydrogen
nuclei are fusing to form helium
nuclei. In the process, some mass
is lost and converted to energy.

A powerful electric current
flows through the plasma. This
heats the plasma and produces a
magnetic field which compresses
the plasma and contains it in the
centre of the torus. The high
temperature and pressure of the
plasma causes fusion.

LISE MEITNER

Austrian-born Lise Meitner (1878-
1968) worked in Berlin from 1907
with a German physicist, Otto Hahn.

In 1938, she had to flee from the Nazis
and went to Sweden. A few months
later, Hahn told her of some puzzling
results he and another German, Fritz
Strassman, had found in an experiment. Meitner
realized that Hahn had split the uranium nucleus. This
was the discovery of nuclear fission. When Hahn
reported the discovery, he gave little credit to Meitner
for her insight. In 1944, Hahn was given the Nobel
Prize for the discovery but Meitner did not share the
prize she rightly deserved.

FUSION ACCELERATOR
Other efforts to produce controlled
nuclear fusion are carried out in
machines called particle beam
accelerators. The most powerful
one is in Albuquerque, United
States. This directs a 100-trillion-
watt pulse of electricity towards a
pea-sized pellet of deuterium gas.
The accelerator sits in a tank of
water. As the beam is fired, electric
sparks cross the surface. The gas is
heated to millions of degrees fora
few billionths of a second - not
enough to start a fusion reaction,
but research is continuing.

Find out more

Atomic structure p.24
Radioactivity p.26
Speed p.1 18
Energy sources p.134
Energy conversion p.138
Current electricity p.148
Magnetism p.1 54
Stars p.278
Fact finder p.408

137

FORCES AND ENERGY

Energy conversion

WHEN LIGHTNING STRIKES, electrical energy is spectacularly
converted into light, sound, and heat energy. This is just one example of
energy changing from one form to another. Energy conversions
' i I, , are continually happening around us. When you press a light

switch, electrical energy is converted into light and heat energy.

A glow-worm converts the chemical energy from its food into
light energy and, if it needs to move, into movement energy.

Energy is converted whenever work is done. When you lift
something heavy, chemical energy in your muscles is converted
into the potential energy of the raised object. The more
work that is done, the more energy that is converted.

Inside the
Sun, nuclear
energy is
converted to
heat and light
energy.

The green leaves of this carrot
convert light energy from the Sun
into the chemical energy
of sugar by a process
called photosynthesis.

If you eat a carrot, the chemical
energy it contains is
transferred to your body.
It is used for activities,
such as breathing and
moving. Winding up an
alarm clock changes this
chemical energy to
elastic potential energy
in the spring.

The remainder of the rocket’s
chemical energy is released as
light and sound energy as
t explodes in the air.

When the rocket is
shooting upwards, it has
kinetic and potential energy,
as well as chemical energy. As
it gets highef, the rocket gains
more potential energy. But its store
of chemical energy gets lower as
the fuel is burned.

EXPLOSIVE ENERGY
Explosives are very powerful stores
of chemical energy. They need not
contain any more energy than other
substances, but they must be able to
release it very quickly. Fireworks
contain explosives. When a rocket
firework, for example, is lit, it soars
into the air and explodes in a colourful
display. The chemical energy of the
explosive has been converted into
kinetic, heat, sound, and light energy.

ENERGY
CHANGES
A drawn bow has
elastic potential
energy. The bow is like a
compressed spring. When
the bow is released, the
potential energy changes to kinetic
energy of the moving arrow. When
the arrow hits the target, we hear a
“thud”; its kinetic energy has changed
into sound energy, and a little heat
energy. This Egyptian wall painting
shows the pharaoh Rameses II.

I nan alarm clock, the potential energy of
the wound spring is converted to movement
energy of its hands and sound energy of its
ticks. The clock keeps working until the

spring is unwound
and has lost its
potential
energy.

Energy chain

Did you realize that your alarm clock is really
powered by the Sun? Energy is seldom changed
directly from its starting form to its final form. It
usually goes through a chain of energy conversions.

The Sun’s energy makes food grow. By eating this food, we create a store of
chemical energy inside us. Among other things, we can use this energy to wind
up an alarm clock. This gives the clock potential energy, which it is able to
change into movement and sound energy.

When a firework rocket is
on the ground, it has a
large amount of chemical
energy but no potential
energy. When ignited, a
stream of hot gas
shoots downwards
and this pushes the
rocket up.

LORD KELVIN

The British physicist William
Thomson (1824-1907) was born in
Belfast, Northern Ireland. He
entered Glasgow University when
k he was just ten years old and

r became a professor at the age of 22.

He helped to found the new science
of thermodynamics, establishing clear
relationships between heat, work, and
energy. He also invented the absolute
temperature scale - the Kelvin scale - and made
important discoveries about electricity and
magnetism. His title became Lord Kelvin after he was
honoured by Queen Victoria.

138

FORCES ANI) ENERGY

If the end ball
is lifted and
dropped, it
hits the line
of balls.

* •

Newton’s cradle

Energy is gradually lost as
sound and heat energy;
each time the balls collide,
there is a clicking noise.
Eventually all the kinetic
energy is converted to
sound and heat, and the
balls stop moving.

Conservation of energy

Energy can be neither created nor destroyed; it can
only be converted into other forms. When energy is
converted, some waste heat is always produced, but if
we take this into account, the total amount of energy is
unchanged. This is called the Principle of Conservation
of Energy. The principle is illustrated by a toy called
Newton’s cradle. Little energy is lost as sound or heat, so
the balls at either end will keep swinging for some time.

USEFUL ENERGY

A steam train produces waste heat
from its funnel. It would be hard
to use this heat energy to
power anything else. Waste
heat is not useful energy; it
is low-quality energy.
Electricity, on the other
hand, is useful; it is high-
quality energy. Whenever
energy changes form, some
high-quality energy is lost. This
means the amount of useful energy
in the Universe is always decreasing.

Dry-cel I batteries, such as
those used in a
torch, waste only
10 per cent of
the energy
they contain.

ENERGY EFFICIENCY
When we use a form of energy to do
work, some of the energy does not go
where we want it to go; it is wasted,
usually as heat. For example, a light bulb
converts only about 5 per cent of the
energy that it consumes into light; the
rest is converted into waste heat. The
efficiency of the light bulb is said to be
5 per cent. No energy converter can ever
be 100 per cent efficient.

A light bulb in an
electric lamp wastes
95 per cent of the
energy it consumes.

The energy is
transferred to
the ball at the
other end.

The ball will
lift and then
swing back
and hit the
line of balls.

A perpetual motion machine
proposed in 1834. The weight of the
balls moving along the arms was
supposed to keep the wheel turning.

PERPETUAL MOTION

Many people have tried
to design machines that
will go on working
forever without an energy
source - a perpetual
motion machine. This is
an impossible dream; all
real machines need a
continuous source of
energy. Not only this,
but they always need
more energy than
they can give out.

A conventional stove
uses valuable energy to
heat the saucepan.

1= ©000©00 J

SAVING ENERGY
We must conserve high-quality
energy sources, such as electricity,
coal, natural gas, and oil as they
are in short supply. Using a
microwave oven is one way of
saving energy because a microwave
oven uses less energy than a
conventional oven to cook food. A
well-insulated house needs less fuel
to heat it, and a machine that is
kept in good condition is able to
work at its maximum efficiency.

A microwave oven
does not waste energy
in heating the plate; it
just heats the food.

Find out more

Chemical reactions p.52
Work and energy p. 132
Energy sources p. 134
Nuclear energy p. 136
Heat p.140

Current electricity p. 148
Thunder and lightning p.257
Factfinder p.408

139

FORCES AND ENERGY

Heat

melted rock

The lava that erupts from a
volcano is molten rock. It is about
600 °C (1,100 °F). This volcano is
on the island of Hawaii in the
Pacific Ocean.

NATURAL THERMOMETERS
Crocuses are natural thermometers.
The flowers open and close as the
temperature rises and falls.

They are very accurate,
reacting to temperature
differences of as little as
0.5°C (0.9°F).

HOW HOT IS IT TODAY? To answer this question exactly, you need a
thermometer, a device which measures temperature. All thermometers
are marked with a scale using two fixed points: the temperature at which
pure ice melts, and the temperature at which pure water boils, at normal
atmospheric pressure. There are three temperature scales: Celsius,
Fahrenheit, and the absolute or Kelvin scale. On the Celsius scale, the
temperature of melting ice is 0°C, and the temperature of boiling water is
100°C. On the Fahrenheit scale, the temperature of melting ice is 32°F
and boiling water is 212°F. The Kelvin scale starts at the lowest possible

temperature theoretically achievable,

called absolute zero. It has degrees
the same size as the Celsius scale.

Heat and

TEMPERATURE
There is a difference
between heat and temperature.

Temperature is a measure of how fast
the molecules in an object are moving. Heat
is the energy that the object has because its
molecules are moving. There is more heat in an
iceberg than in a cup of boiling water, even though
the water has a higher temperature. This is because
the iceberg, although colder, is much larger.

GABRIEL

FAHRENHEIT AND
ANDERS CELSIUS

The Fahrenheit
thermometer was
invented by Gabriel
Daniel Fahrenheit
(1686-1736). He was a
Anders Celsius German physicist who
settled in Amsterdam,
Holland, where he worked as an
instrument maker. Anders Celsius
(1701-44) invented the Celsius scale.
He realized the value of using a
thermometer with 100 degrees
between the freezing and boiling
points of water. He was a professor of
astronomy at Uppsala, Sweden. His
favourite subject was the aurora
borealis, a display of lights seen in the
sky around the North Pole.

Meter to
measure
temperature

Electric
filament
changes colour to match the
colour of the hot object.

MEASURING HIGH TEMPERATURES
A pyrometer is used to measure very high
temperatures such as those of lava flowing from a
volcano or the inside of a glass-making furnace.

The word “py rometer ” means fire measurer.

Things glow a different colour according to how
hot they are. A pyrometer contains an electric
filament and compares the colour of an object
with the colour of the filament. An electric current
heats the filament until its colour matches the
glowing object. The temperature is then found by
measuring the electric current.

PRESS-ON THERMOMETER
Liquid crystals have molecules
arranged in rows like those in a crystal
but they flow like a liquid. Some
change colour according to
temperature and are used in strip
thermometers to take the
temperature of small children and
babies. Heat rearranges the molecules
making it easy for light to pass
through the liquid. A different colour
then glows according to the
temperature of the child.

140

FORCES AND ENERGY

Effects of heat

Most substances expand (become larger) as they get hotter
and contract (become smaller) as they cool. A 1,4(30 m .
(4,600 ft-)long bridge can be half a metre (1.5 ft) longer in
summer than in winter. When a substance is heated, the
energy it absorbs makes its molecules move faster and
further and they take up more room. Changing the
temperature enough makes a substance change from one
state to another. If a solid is heated to a high enough
temperature, it will melt; if a liquid is heated to a high
enough temperature, it will boil and become a gas or vapour.

Boiling water will
not get any hotter
even if it is still
being heated.

HIDDEN HEAT
When a liquid
changes to a
vapour, it absorbs
heat without
increasing its
temperature. The heat
energy is used to change
the liquid into vapour and is
stored in the vapour. It is called latent
(hidden) heat. When the vapour condenses
into liquid, the latent heat is released,
warming the surroundings. Latent heat is
also absorbed when a solid melts, and
released when the liquid freezes.

Cork seals the
flask so that air
cannot escape ._

Water rises up
the tube when
the flask has
been heated in
a pair of hands.

Glass tube goes
through the cork
into the water.

EXPANDING GASES
Gases expand about 1,000 times more
than solids and 10 to 100 times more
than liquids. If the temperature of a
gas doubles, then its volume doubles.
This flask was half-filled with cold
water, sealed, and heated gently in a
pair of hands. The air inside the flask
expanded and pushed the water up
the tube.

Iron

Wire firmly
secured in a
wooden block.

Knitting needle
turns the pointer
as the expanding
wire makes it roll
round.

Weight holds
the wire
down.

EXPANSION METER

This expansion experiment shows how a thick wire
expands when heated. Candles heat the wire at
one end, and as the wire expands it rolls a knitting
needle which turns a pointer across a dial.

Temperature
regulator

PAIN RELIEF

This athlete is being treated with
a pain-relief spray. The spray
contains a substance which
evaporates (turns to vapour) very
quickly. The latent heat needed for
it to evaporate is taken from the
athlete’s hand. The hand cools and
the pain is reduced. Sweating
makes you cooler in the same way.
As the sweat evaporates, it absorbs
heat from your body.

AIR CONDITIONER

An air conditioner works by evaporation. A liquid called
a refrigerant is allowed to evaporate to form a gas inside
cooling pipes. The evaporating liquid absorbs heat from
air inside the building. The gas is then compressed and
turned back into a liquid. This process, which takes place
outside the building, releases the heat absorbed from the
air. The cool air then
returns to the room.

Heat released
outside

Inside

Outside

When the
contact
breaks,
the heating
is turned off.

As the strip
heats up, the
brass expands
more than the iron,
and the strip has to
bend.

Electric current
to heater

UNEQUAL EXPANSION
Metals expand at different rates
and this fact is used to make a
thermostat work. A thermostat
keeps temperature at a steady level.
It contains a bi-metallic strip - a
strip made of two different metals,
often brass and iron. In a heating
thermostat, the bi-metallic strip
bends as it gets hotter and breaks
an electrical contact when the
room has reached the required
temperature.

Find out more

Changes of state p.20
Kinetic theory p.50
Behaviour of gases p. 51
Colour p.202
Volcanoes p.216
Fact finder p.408

141

FORCES AND ENERGY

Heat transfer

If YOU STAND NEAR A FIRE, heat enters your body from
your surroundings. If you are outside on a freezing day,
heat escapes from your body into the cold air around you.
Heat always travels from something hot to something cold,
or from a hot part of something to a cold part. There are
three ways that heat can travel: by convection, conduction,
or radiation. Convection is how heat travels in moving
currents through liquids and gases. Conduction is how heat
travels through solids. When one part of a substance is
heated, its molecules start to vibrate more violently. They

knock against their
neighbours and pass their
energy on. Radiation is how
heat travels through empty
space by electromagnetic
waves. This is how heat gets to
the Earth from the Sun.

RADIATION

All objects emit heat radiation, also
called infrared radiation. The hotter
the object, the more radiation it
emits. Infrared radiation travels at the
same speed as light, but has a longer
wavelength. Like light waves, infrared radiation is reflected by shiny surfaces and
absorbed by dark surfaces. We cannot see infrared rays but cameras with special
film can take infrared photographs called thermographs. Different colours
indicate different amounts of heat radiating out. The hottest bit shows as white.

Cavity wall filled
with foam
polystyrene

Fibreglass
insulation in the
roof and the loft

Air trapped in a
space under the
floorboards

Air trapped
between two panes
of glass in double-
glazed window

Carpet on
the floor

SAVING HEAT
It is easy for heat to
escape from a
building. Over one-
third of the heat is lost
through the walls, a
quarter is lost through the
roof, and the rest escapes
through the floors and windows. To
prevent these losses, buildings need to be well insulated.

Metal - a good
conductor.

Wood - a poor
conductor, _—

CONVECTION
When the land gets hot, it heats the air
above it. The heated air rises
because it expands and becomes
less dense. Cooler air falls down to
take its place. A continuous current
of rising and falling air, called a
convection current, is set up.

Gliders and birds use convection
currents called thermals to lift them
up in the air.

Marble - a good
conductor

Plastic - a poor
conductor -

RIGHT FOR THE CLIMATE
Many animals have shapes and colours to
suit the climate in which they live. The
fennec fox lives in the North African
desert. During the day, the fox’s pale fur
does not absorb much heat radiation and
its huge ears transfer heat to the air by
convection. At night, when it is cold, the
fox’s f ur traps air, which stops too much
heat escaping f rom its body by conduction.

Vacuum

VACUUM FLASK

The vacuum flask was invented by
Scottish scientist James Dewar
(1842-1923). It keeps hot drinks hot,
or cold drinks cold, by stopping the
transfer of heat. The flask consists of
a glass bottle with double walls. A
vacuum between the walls stops
conduction and convection.
Radiation is prevented by silvering
the walls. The stopper is made of a good
insulator such as cork or hollow plastic.

conductors do not
feel cold when
you touch them
because they do
not take the heat
from your hand
quickly.

CONDUCTION
Different materials
conduct heat by different
amounts. Metals are the
best conductors. Saucepans
are made of metal so that they heat
up quickly. Saucepan handles are
made of wood or plastic which are
poor conductors. Water is a poor
conductor; cork and fibreglass are
poor conductors because they are
mainly air, and gases are the worst
conductors of all.

Find out more

Heat p.140

Electromagnetic spectrum
p.192

Winds p.254

Formation of clouds p.262
Deserts p.390
Factfinber p.408

142

FORCES AND ENERGY

Engines

GEORGE STEPHENSON

The first successsful steam locomotive
was built by British engineer George
Stephenson (1781-1848). He began his
career caring for the engines and
pumps in the mines near Newcastle,

England. In 1825, he set up a locomotive
factory where he designed and built the
first locomotive to pull a passenger train,
the world’s first public railway between Darlington and
Stockton. Stephenson’s most famous locomotive was
called the Rocket. In 1829, it won a competition,
reaching a speed of 46 km/h (29 mph). It was then used
on the Liverpool to Manchester line.

Furnace

Cylinder

STEAM ENGINE

Because the fuel is burned outside the cylinder, in a furnace, a steam
engine is called an external combustion engine. Hot gases produced by
burning coal flow through a boiler and heat water, making steam. The
steam is heated, until it is at high pressure and temperature, and fed to
the cylinder. There it expands, forcing the piston along. I n a locomotive,
the moving piston turns the wheels.

Distributor
feeds high-
voltage
electricity to
the spark
plugs.

Channels for
cooling water.

Clutch
disconnects
the engine
when
changing
gear.

Crankshaft turns
the wheels,
via the clutch
and gearbox.

It is

connected to
the camshaft
so that the
valves open
at the
correct

Camshaft controls
the opening and
closing of valves.

Valves let fuel into
the cylinder and

Belt drives a

Fan belt
drives a
cooling fan.

The ROCKET is the most powerful engine.
It can lift a heavy spacecraft off the ground
and send it into space. Aircraft, cars, boats,
motorcycles, and many other machines are
driven by a petrol or diesel engine. Without
engines, we would have to rely on our own
strength and the strength of animals for
transport and industry. Every engine
converts energy from some sort of fuel into
movement. They work on the principle that
a hot gas expands. Fuel is burnt to heat gas
and the expansion of the gas is harnessed to
drive the machine. Some engines have
pistons which move back and forth inside
cylinders. They are called reciprocating
engines. Other engines do not have pistons.

Exhaust

port

Cylinder

drive the crankshaft.

^Sparkplug

Transfer

port

1. Induction -
Piston descends,
sucking in fuel and
air through the
open inlet valve.

2. Compression -
Piston ascends,
compressing the
fuel mixture. Both
valves are closed.

3. Power - Spark
plug ignites the
mixture. The
exploding fuel
forces piston down.

4. Exhaust - Piston
ascends, forcing the
burnt fuel out
through the open
exhaust valve.

INTERNAL COMBUSTION ENGINE

A car engine is called an internal combustion engine because the fuel is
burnt inside a cylinder (“combustion” meaning burning). Most cars have
a four-stroke engine. They produce their power with four movements, or
strokes, of the piston. Engines have between four and eight cylinders
which move in sequence to produce a continuous output of power.

Water turned to steam in

High-pressure
steam fed into

1. Piston rises, sucking
fuel mixture into the
lower part of the
engine. The piston
compresses the fuel
already in the cylinder.
A spark explodes the
mixture when it is fully
compressed.

2. Piston

descends, pushing
new fuel into the
cylinder through
the transfer port.
The burnt fuel is
pushed out through
the exhaust port.

TWO-STROKE ENGINE
Motor cycles have two-stroke
engines. These engines are
small and powerful but they
are noisy. They have no
valves. Instead there are
openings, called ports, in the side of the
cylinder. The moving piston opens and
closes the ports.

143

Continued on next page

Continued from previous page

FORCES AND ENERGY

Oxidizer

blades, where the
pressure is highest,
are smaller than
those at the ends.

Pump

Valves

Combustion

chamber

ROCKET
The simplest kind
of engine is the
rocket. It burns fuel
in a combustion
chamber. The hot gases
produced expand and
stream out from a nozzle
at the bottom, thrusting the
rocket upwards at great
speed. Some spacecraft are
launched using solid-fuel
booster rockets which are like
huge firework rockets. Other
rockets use a liquid fuel, such as
kerosene, which is burnt with
another liquid called an oxidizer. The
Space Shuttle has three liquid-
fuelled rocket engines. Together,
they burn 98 tonnes of fuel in a

Stationary blades are fixed to the
inner wall to direct the steam on to
the blades of each wheel at

the right angle.

STEAM TURBINE
In its simplest form, a turbine is
a wheel with blades mounted
on an axle. It can be driven by
gas, steam, or water. Steam
turbines are used in power
stations. Steam is driven at high
pressure against the blades to
turn the turbine which is
connected to the electricity
generator. Multi-stage turbines
are most efficient, taking nearly
all the energy from the steam.

Rocket speeds forwards
in reaction to the
gases shooting out
backwards.

Some

air bypasses
the main part
of the

JET ENGINE
Most modern high-speed
aircraft are powered by a jet engine.

Fans at the f ront of a jet engine spin and suck air
into the engine. Inside, more fans compress the air and
at high pressure into the combustion chamber. Here, burning liquid
fuel heats the air, which expands and rushes towards the tail of the
engine. As the air streams out, it spins a turbine which drives the fans at
the front. In a turbofan engine, shown here, some air flows through a
duct around the main part of the engine. This means there is more air
flowing through, giving the engine extra thrust.

...Hot gases

FRANK
WHITTLE

English test
pilot and
engineer Frank
Whittle (1907-1996)
invented the jet
engine in 1929. He tried
to persuade the British Air Ministry
that his engine would work, but his
ideas were rejected. He set up his
own company to make the new
engine and, by 1937, the first
engine had been built and tested
on the ground. In 1941, an
experimental aircraft with a Whittle
engine made its first flight.

Liquid
fuel

Air sucked
in by
spinning
fan.

Combustion

chamber

Fans called compressors
increase the pressure of the
air and push it into the

Hot air and exhaust
stream out over a

ENGINE DEVELOPMENT

1712 Thomas Newcomen builds
the first steam engine to use a
cylinder and piston.

1765 James Watt builds a steam
engine six times as powerful as
the Newcomen engine.

1800 Richard Trevithick builds
the first high-pressure steam
engine.

1860 Etienne Lenoir designs the
first internal combustion engine,
using coal gas and air as fuel.

1877 Nikolaus Otto develops the
four-stroke engine.

1883 Gottlieb Daimler builds the
first petrol engine.

1884 Charles Parsons builds the
first steam turbine to generate
electricity.

1926 Robert Goddard launches
the first liquid-fuel-propelled
rocket.

1930 Frank Whittle patents the
jet engine.

JET PROPULSION
This toy car uses jet propulsion to speed along the floor.
A balloon is attached to the car and filled with air. When
a valve is opened, air rushes out
backwards through the neck
of the balloon, thrusting the
car forwards.

Find out more

Bel

For

Eli

tAVIOUR OF GASES 1

CES AND MOTION P

)RK AND ENERGY P.]
JERGY SOURCES P.L
ECTRIC MOTORS P.l

Rockets p.299

p.51

.120

132

144

ELECTRICITY and MAGNETISM

Almost anywhere you go, you will find electricity at work,

and often magnetism too. Electricity and magnetism have
completely changed our lives. Generators use magnetism to
produce electricity from motion, so that light and heat are
available at the flick of a switch. Electric motors use magnetism
to change electricity into motion, so that machines can do
tedious work for us, such as washing clothes. Other motorized
machines, such as electric drills, help us to carry out tasks quickly
and with little effort. Electronics (the use of components, or parts
for controlling electricity in various ways) allows
us to use electricity and magnetism in many
ways, as in radio, radar, and computers.

Versatile energy

Electricity is easily generated,
transmitted to where it is needed,
and converted into other forms of
energy. In an office, for example, a
fan changes electricity into motion,
and a bulb changes electricity into
light. A telephone changes
electricity into sounds, and also
changes sounds into electricity.
And a computer changes a steady,
supply of electricity into pulses to
carry out its tasks.

Since electric light
bulbs were first usee
in the late 1800s,
they have been
made much more
reliable and efficient.

ELECTRONICS THAT CARE
People who are very ill often need constant
attention in hospital. Instead of a nurse sitting
at the bedside, electronic equipment monitors
(constantly checks) their condition. If, for
example, a patient’s breathing or heartbeat
changes, the equipment sounds an alarm to
tell nurses and doctors that they are needed.

Electricity
helps to make
our surroundings
more comfortable.

The motor in an electric
fan makes the blades
turn round to
send out a
stream of air.

LODF.STONE

Found in the Earth, lodestone
is a mineral that is naturally
magnetized. It is a form of the
mineral magnetite. Iron filings
near it become magnetized and
stick to it. Some early sailors used a
piece of lodestone, suspended from
a string, as a magnetic compass.

A modern
telephone
does more
than let us
talk to people.

Its electronic memory can
store different numbers so
that we can call them by
pressing a single button.

MODERN MAGNETS
Now that the nature of magnetism
is understood, powerful magnets
of various shapes can be made
from steel. The best magnets
are made from steel alloys
(metal mixtures) specially
designed to keep
their magnetism.

Steel pins can be
temporarily
magnetized, which
allows them to be
picked up with a
magnet.

Today’s cheap pocket
calculator would have amazed
scientists in the early 1950s.
Then, a whole room full of
valves and other bulky
components would have been
necessary to make a calculator.

ANCIENT
ELECTRICITY
Around 600 ii.c:.,
an Ancient Greek
philosopher (thinker)
called Thales of Miletus
™ found that when he rubbed a
piece of amber with a doth, feathers
and other light objects stuck to it. We now
know that the amber had become electrically
charged by friction. The word “electricity”
comes from the Greek for amber - elektron.

Until the mid-
1970s, most
people had never
seen a computer.
Now computers are
almost everywhere. The
principles of computing were
set out more than 150 years ago,
but electronic computers could only
be made for everyone to buy when the
complex circuits could be made small enough.

“ELECTRICS” AND “NON-ELECTRICS”
William Gilbert (1544-1603) did
outstanding work in magnetism and
electricity. He showed that the Earth must
be like a magnet to affect compasses. He
recognized the difference between
electrical insulators and conductors, and
called them “electrics” and “non-electrics”.

145

ELECTRICITY AND MAGNETISM

Static electricity

electrostatic

INDUCTION
You can use a plastic spoon
to make a stream of water
from the tap flow sideways
by rubbing the spoon on
yourclothes. Negative
charges on the spoon
repel negative charges in
the water to the far side
and attract positive
charges in the near
side. The spoon
induces these

to\ b ^mper C because THE CRACKLING NOISE you sometimes hear
rubbing the two w hen you pull your jumper off over your head

together gives each , ■ , . . J rr . , . ,

one an opposite happens because of static electricity. If it s dark,

charge. y OU can see fl as h es Q f light as well. Static electricity
is electricity that doesn’t move. The crackles and
flashes are the static electricity suddenly flowing
away; this is discharging. You sometimes get an
electric shock from touching a doorknob, because
the static electricity that builds up in your body
suddenly flows from your hand to the doorknob.

Lightning is static electricity suddenly discharging cha [ sed regions
between clouds or between clouds and the the effect is

ground. Static electricity builds up with friction, called electrostatic
when two different materials rub together.

Charging by friction

A 11 1 • , r «. 1 . These two balloons

All objects are made of atoms. Each atom

has equal numbers of electrons and

protons. Electrons have a negative charge;

protons have a positive charge. These

charges balance each other exactly to

make objects neutral (uncharged).

But friction, like rubbing a balloon $

on your jumper, makes electrons A I

rub off from your jumper onto A I

the balloon. This charges the I

balloon with static electricity. if I

It now has more electrons ^g]

than protons, so it is #BP REPULSION

negatively charged. And i Two charged balloons hang side by side on

your jumper, with more j - ’Js threads attached to the same point. They

protons than electrons, is f repel each other because they are both

positively charged. negatively charged. If they were both neutral,

they would hang next to each other.

have been charged
by being rubbed #
on a jumper. |lf|rn il

The charges
were built up
on the spoon
by friction.

ATTRACTION
A balloon that has been charged
by f riction will attract small pieces
of paper. Like charges repel each
other, so the negative charges on the
balloon force away the negative charges

in the paper. The parts of the paper
closest to the balloon become
positively charged. They stick
_ to the negatively charged
balloon because opposite
charges attract.

A comb, negatively charged by passing
it through hair, repels negative charges
to the leaves, making them deflect
(alter their direction).

PHOTOCOPIER

Many photocopiers work by using static
electricity. An image of the original
forms on the large drum inside the
machine as invisible positive charges.
These attract particles of fine black
powder, the toner, producing a visible
image on the drum. The toner is then
transferred to electrically charged paper
as it passes round the drum. Heated
rollers melt the toner, so that it sticks to
the paper and forms a permanent image.

3. Heated rollers
bond toner
image to paper.

2. Toner image
transfers to

ELECTROSCOPE
The gold-leaf electroscope is an
instrument that can show whether or not
an object is charged. If you bring a
charged object near the metal plate at
the top, the gold leaves are both given
the same charge by induction. Since like
charges repel each other, the hinged
leaves spread apart. Gold leaves are
extremely thin and light. They are used
] to make the electroscope very sensitive.

1. Toner is attracted to invisible
charges on the

146

ELECTRICITY AND MAGNETISM

Charges

WITHIN A CLOUD
High in the air, in the
clouds, swirling ice
particles become
charged with static
electricity. The top of
the cloud becomes
positively chargedj and
the bottom of the cloud
becomes negatively
charged. Sometimes this
electricity discharges
as a flash of
lightning inside
the cloud to
V balance out the
Wp charges once more.

The lighter
particles with
positive
charges are
swept
upwards.

GIANT SPARKS

A fork of lightning flashing across the sky is
a giant spark leaping between the ground
and a cloud. As well as giving out a very
bright light, lightning is very hot. The air
around it heats up and therefore expands
so quickly that it explodes, causing thunder.

The larger, negatively
charged particles cluster
at the bottom of a cloud.

if \ BENJAMIN

M Hgf FRANKLIN

P ^ X American

K ®§; statesman, author,

printer, and
inventor Benjamin
Franklin (1706-90)
showed that lightning
* is caused by electricity
by carrying out a very
dangerous experiment. In 1752, he
flew a kite in a thunderstorm.
Electricity passed down the damp
string to a key at the other end.
When he put a finger near the key, a
spark jumped between them.
Franklin concluded that electricity
in clouds caused the spark and that
lightning is a kind of spark too. In
1753, he announced his invention
of the lightning conductor.

The top of the
lightning conductor
is pointed, and the
lower end is
connected by wire
to the ground.

The negative charge on
the underside of a cloud
induces a positive
charge on the surface
of the ground below.

Brass rod
connected to
chain, which
contacts the
inner foil.

++++

Rubber

stopper

HOW LIGHTNING STRIKES
If the charges in the cloud are
strong enough, they force a path to
the ground through the air and
discharge as a lightning flash. Tall
buildings, trees, and people on
open ground are prime targets for
lightning because they provide a
convenient path for the discharge.

LIGHTNING CONDUCTOR
Most tall buildings have a metal
rod called a lightning conductor on
the roof. A wire connects the rod to
the ground. The negative charges
on the underside of the cloud
attract positive charges from the
ground. A stream of these positive
charges flows up to the cloud,
where they cancel out some of the
negative charges. This may prevent
lightning from striking, but if
lightning does strike, the electricity
flows harmlessly through the rod
and wire.

Metal foil
plates ,

Insulator ,

Connecting
wires are
welded to
the plates.

Glass jar

Inner foil

Outer foil

CAPACITORS
Devices called capacitors are
used to store an electric charge
in electronic equipment such as
televisions and computers. For
example, electricity supplied as
brief pulses is stored in a
capacitor so that a steady current
can be given out from it. Inside
some capacitors, metal foil plates
are separated by thin plastic, all
rolled up and sealed.

LEYDEN JAR

Early experimenters sometimes
stored electricity in a device called a
Leyden jar. It was named after the
Dutch city where the jar was First
used, in 1745. One form consists of
a glass jar with a coating of tin foil
inside and outside. A metal rod
connects to the inner foil. An
electric charge can be stored on the
tin foil plates. This Leyden jar was
an early form of capacitor.

Find out more

Atomic structure p.25
Current electricity p. 148
Electronic

COMPONENTS P.168

Thunder and
LIGHTNING P.257

147

ELECTRICITY AND MAGNETISM

Current electricity

Almost everywhere we go we can see

current electricity at work. Bulbs change electricity
into light, electric heaters change electricity into
heat, and electric motors change electricity into
motion. Electricity is a form of energy, and it has so
many uses because it is easily changed into other
forms of energy. Electricity is also very easy to
use because it can flow along wires to wherever
we need it. We call this flow an electric current.

The flow is measured in units called amperes
or amps. Most electric currents consist of a
stream of electrons, but some currents
consist of other kinds of charged
particles, called ions.

A microphone converts
sounds into electric signals
and sends them to the amplifiers.

FREE ELECTRONS
Electricity can flow
through a metal, such as
copper, because the metal
contains electrons that are
free to move from one
atom to another.

Speakers
convert electric
signals received
from the amplifiers
back into sound.

ROUND AND ROUND
Using marbles, you can
demonstrate how an electric
current flows. If you push a
circle of touching marbles,
they all move at once. The
one at the other end moves as
soon as you touch the first
marble. A battery forces
electrons along wires in a
similar way to make an electric
current flow.

Positive
terminal (+)

Negative
terminal (-)

Electron flow

The bare overhead
cables are supported
using insulators.

In an insulator,
all the electrons stay
with their own atoms, so
electricity cannot flow through it.

Conductors and insuiators

Copper wires in electrical cables are
called conductors because they
conduct an electric current, which
means that they allow it to pass
through them. Around the copper
wires is plastic, which does not
conduct electricity because it has no
free electrons. It is called an
insulator. It prevents electricity
flowing where it is not wanted.

The cables and
the arms conduct
electricity.

ELECTRON
FLOW

People used lo think electricity flowed
around a circuit from a battery’s
positive terminal to its negative one.
Many useful ruleswere worked out
using this idea, so current is still shown
like this. This is called conventional
current. In fact, electrons flow from the
negative terminal to the positive one.

OVERHEAD SUPPLIES
Some electric trains pick up electricity
using arms that slide along cables above the
track. These cables must be bare
(uninsulated), so that the arms can make
electrical contact with them. Current flows
to the motor that drives the train. The
overhead cables have to be supported using
insulators. This prevents electricity from
being wasted or dangerous. Conductors
and insulators are used together to make
electricity safe and efficient.

Lights convert
electricity into light.

The video screen
converts electric signals
received from the
cameras into pictures.

ELECTRICITY IN ACTION
At a pop concert, electrical
equipment produces spectacular
lighting effects and loud sounds.
People a long way from the stage can
watch the musicians on the huge
screens around the stadium.

The pick-up of the
electric guitar changes
string vibrations into
electric signals and
sends them to the
amplifier.

The TV camera
converts pictures into
electric signals.

148

ELECTRICITY AND MAGNETISM

ALEX MULLER

The main problem
with superconductors
is that they have to be
kept at close to absolute
zero. This is the lowest
possible temperature,
0K(-273°C, -460°F).
But Swiss physicist Alex
Muller (born 1927), helped
by Georg Bednorz (born 1950), found
that a copper oxide ceramic material
containing barium and lanthanum can
superconduct at 35 K (-238°C, -396°F).
They won the Nobel Prize for Physics in
1987. By 1988, others had made a
ceramic material superconduct at 123 K
(-150°C, -238°F). But no one has yet
made a superconductor that works at
room temperature.

insulation

Outer coating and
steel pipe protect all
the wires inside.

These

superconducting
wires are made
of a special
ceramic covered
in silver.

SUPERCONDUCTING CABLES

A material that conducts electricity well has little resistance
to the flow of current. In certain metals, such as tin and
lead, and some ceramics, the resistance becomes almost
zero when they are cooled to a very low temperature. In
other words, they become superconductors (almost perfect
conductors). Superconductors would be ideal as electricity
supply cables, as they would waste hardly any power. But
they need to be kept cool with liquid nitrogen or liquid
helium, and this is expensive to install and run.
Experiments are being done to find superconductors that
work at higher temperatures.

A crystal of
pure silicon

Ions, which are
positively charged,
are attracted to the
metal, which is
negatively charged.

ELECTROPLATING

These printed circuit boards have been dipped
into a solution of copper sulphate. Electricity is run
through the solution and the circuit boards. The
boards form the anode in the circuit, so the copper
ions are attracted to them and become attached to
the board to make the copper tracks.

CHARLES AUGUSTIN COULOMB
Coulomb (1736-1806) was a French
physicist, inventor, and engineer. His
most important work involved
friction, magnetism, and electricity.

I Ie devised sensitive instruments for
measuring the forces between
magnets and between electric
charges. The unit for measuring an
amount, or charge, of electricity is
named after him. One coulomb
(symbol C) is the amount of electricity
that flows past any point when a current
of one amp flows for one second.

A vacuum helps
to keep the
temperature

Liquid nitrogen
runs round the
three conductors.

Liquid nitrogen runs
through the copper tube to
keep the temperature of
the wires at 77 K (-1967 C,
-321° F), the temperature
at which the ceramic

ELECTRICITY AND IONS

A current can flow through a solution not as electrons,
but as charged particles called ions. Electroplating is a
way of covering an object with a layer of metal using
electricity. The object to be coated is connected to the
negative side of the electricity supply, which makes it
the negative electrode. It attracts positively charged
ions (for example silver, copper, or zinc ions) and
therefore becomes coated (electroplated) with silver,
copper, or zinc.

Find out more

Properties of matter i>.2 £ 2
Atomic: structure p.24
Semimetals p.39
Electroiasis p.67
Cells and batteries p. 150
Electronic

COMPONENTS P.168

Fact finder p.4 10

PURE SILICON
In pure silicon, there are four
electrons for each of the silicon
atoms. The charges of the electrons
balance out four positive charges in
each nucleus, so silicon is neutral.

Atom

P-TYPE SEMICONDUCTOR
Boron has only three electrons per
atom. So if small amounts of boron are
added to silicon, this leaves holes,
which makes the material positive, and
gives a p-type semiconductor.

0 0

® H o

0 0 o o 0 o

O 0

- o ©

Q # o.

0 6 0 0

0 '

o ° ©

o ©

O • °

o| O O 0 o

o o

N-TYPE SEMICONDUCTOR
Arsenic and phosphorus have five
electrons per atom. So adding a
trace of either to silicon introduces
free electrons. This gives an n-type
semiconductor.

Semiconductors

Materials that do not
conduct electricity very well
are called semiconductors or semimetals. They are
used to control current in electronic equipment.
Silicon is the most common semiconductor. It is
doped (made impure) with tiny amounts of arsenic,
phosphorus, or boron to alter its electrical
properties and make n-type (negative) or p-type
(positive) semiconductors. In n-type
semiconductors, electrons carry the current, and in
p-type semiconductors holes carry the current.
Semiconductors are used to make electronic
devices such as silicon chips for computers.

149

ELECTRICITY AND MAGNETISM

Cells and batteries

DRYCELLS

Ordinary dry cells are used in
most torch batteries. Common
dry cells use ammonium chloride
as the electrolyte. Cells needed to
supply heavier currents use zinc
chloride. Alkaline cells, which last
longer and can supply even
heavier currents, use the alkali
potassium hydroxide.

How MANY BATTERY-OPERATED devices
are there in your home? Radios, torches,
toys, clocks, and watches are a few of the
more common items that use batteries.
Batteries come in many shapes and sizes.
Some are little bigger than a pill, while
others are too heavy for a person to lift.

But most batteries have one thing in
common: they store chemical energy and
change it to electrical energy. A cell is
the basic unit that produces electricity,
and a battery has two or more cells.

But we often use the word battery when
talking about a single cell too, like a dry
cell. The pill-sized battery in a watch is a cell.
Cells act like pumps to force electrons to flow
along conductors.

Positive

Electrons
from the
negative
terminal up to
the positive
terminal.

Actual size

MERCURY
OXIDE CELL
Many electronic
watches run on
a single
mercury oxide
cell. This type
provides a
steady 1.35-volt
supply over a
long period.

Inside a cell

A typical cell has three main
parts. There is a negative
electrode, a positive electrode,
and between these is a chemical,
or a mixture of chemicals, called
the electrolyte. This is a moist
paste or a liquid that conducts
electricity because the chemicals
in it split into charged groups of
atoms called ions. Chemical
reactions in the cell cause
electrons to flow out of the
negative electrode, through the
device being powered and back
via the positive electrode.

NICKEL CADMIUM CELL
Unlike common cells,
nickel cadmium cells can
be recharged when they
have run down. This makes
running a battery-powered
toy much cheaper.

Electricity
flows through
the bulb and
makes it glow.

Actual size ,

Negative
terminal (-)

INSIDE A DRY CELL
The most common kind ol' cell
is called a dry cell. It works like
the cell invented by French
engineer Georges Leclanche
in 1865. His cell had a liquid
electrolyte, but in the modern
version the electrolyte is a moist
paste. The electrolyte is the
ammonium chloride paste.

The powdered carbon and
manganese (IV) oxide prevent
hydrogen from forming on the
carbon rod, which would stop
the cell from working normally.

Zinc casing,
which acts as
the negative
electrode.

Carbon rod,
which acts as
the positive
electrode.

Powdered
carbon and
manganese
(IV) oxide

Ammonium
chloride paste
is the

electrolyte.

ELECTROMOTIVE FORCE

f~. .'A

The electrical force of a cell or battery is
called its electromotive force (e.m.f.). This
force, which makes electrons flow around
a circuit, is measured in units called volts
(symbol V). Each kind of cell has a
particular e.m.f. A dry cell, for example,
has an e.m.f. of 1.5 volts.

ALESSANDRO VOLTA

An Italian count called Alessandro
Volta (1745-1827) invented the first
battery. Each cell had a copper disc
and a zinc disc for the electrodes.
Between them was a piece of cloth
soaked in salt solution. This was the
electrolyte. Each cell had a small e.m.f.
But Volta found that a pile of these cells
gave a large e.m.f. This, the first true
battery, is known as Volta’s pile, or a Voltaic pile. The
volt, the unit for electromotive force, is named after him.

150

ELECTRICITY AND MAGNETISM

Cell size

Most electric torches take
two or more dry cells. As in
Volta’s pile, the cells are
connected in series, or one
after the other. This increases
the total e.m.f. For example,
two 1.5-volt cells in series have
a total e.m.f. of 3 volts. A
larger e.m.f. can force a larger
current around a circuit.

Large, powerful torches may
take four or more cells. The
size of a cell itself has no effect
on its e.m.f. The chemicals in the
cell determine its e.m.f. But large
cells last longer than small cells of
the same basic type.

Some small
radios take a
9-volt dry
battery. This
contains six
1.5-volt dry
cells, in a pile,
like the cells in
Volta’s first
battery.

These
two torches
both use a
3-volt bulb
because the
batteries in
each torch
produce an
e.m.f. of
3 volts.

LEMON CELL
You can make a simple cell by pushing
objects made of two different metals into a
lemon. The metals are the electrodes of the
cell. The lemon juice, which is a weak acid,
is the electrolyte. A piece of zinc and a
piece of copper wire work well as electrodes.

The e.m.f. produced lights up an
LED (light-emitting diode).

Muscles
used for
swimming

Spinal cord

Muscles

The electric
organs make
up most of the
fish's body.

ELECTRIC EEL
All animals have a bit of electricity in their
nerves and muscles. Some animals, such as

SOLAR CELLS

Unlike ordinary cells, solar cells do not use chemical
energy. Instead, they change light energy into
electricity. Solar cells are also known as
photovoltaic (light-voltage) cells. Small solar
cells power some pocket calculators. In some
places, such as Antarctica, where there is no
mains electricity supply, big panels ugftt
containing many solar cells are
sometimes used instead. Most
solar cells are devices
called silicon diodes.

When light hits the
area where the two
types of semiconductor
join, electrons flow
through the cell as an
electric current.

N-type semiconductor

P-type semiconductor

the electric eel (Electrophorus elect icus) from
South America, can produce a powerful blast of
electricity, which they use to kill their prey. The organ
that produces electricity takes up most of the eel’s body,
and is made of special muscles. Electricity is built up in
the organ by the movement of ions, and then timed to
discharge all at once to produce a voltage high enough
to stun fish swimming nearby. In some electric eels this
voltage can reach 650 volts - enough to stun a person.

ELECTRIC CAR
This car has a battery for use in towns
and a petrol engine to keep the battery
powered up for longer journeys.
Some prototype electric cars run
on batteries only, but the
batteries tend to be large
and not last long enough.

The batteries are
recharged overnight on
mains electricity, making
the most of a time when
few people are using
electricity. The great
advantage of battery-

» powered cars is that they

produce much less air pollution
than those that use petrol or diesel
engines. So they are an important way of
dealing with pollution problems.

Lead!

dioxide

plate

Lead,

plate

Sulphuric acid

Electricity is produced in the reactions
between the plates and the sulphuric acid.

CAR BATTERY
Most cars have a 12-volt battery
containing six 2-volt lead-acid cells. Each
cell consists of a lead plate, a lead dioxide
plate, and sulphuric acid. Unlike dry cells,
lead-acid cells can be recharged with electricity
after use. So the battery does not have to be
replaced unless it becomes faulty. Cells that cannot
be recharged are called primary cells; cells that can
be recharged are called secondary cells. The lead-
acid battery powers the car’s electrical system. It is
recharged by a device in a car called the alternator.

Find out more

Bonding p.28
Transition metals p.36
Sf.mimetals p.39
Electrolysis p.67
Energy sources p.134
Generators p.159
Light p.190
Muscles p.355
Factfinder p.410

151

ELECTRICITY ANI) MAGNETISM

Circuits

Multimeter switched to 250-
milliamp range and connected
in series with this branch of
the circuit shows that the
current flowing is 165 mA.

Switch controls
current flow through
entire circuit.

Crocodile clip

Resistor causes
voltage drop of 7.5
volts, so that remaining
voltage (6 volts) is
correct for the bulb in
this part of the circuit.

Switch controls
current flowing
through this branch
of the circuit.

Multimeter switched
to 10-volt range
shows that the
voltage across the
bulb is 5 volts.

Switch controls
current flowing
through this
branch of the
circuit.

The voltmeter is a
moving coil meter with
a high-value resistor in
series. The resistor
prevents the voltmeter
from taking a large
current and changing
the circuit conditions.

The ammeter is a
moving coil meter with
a low-value resistor in
parallel. The ammeter
hardly reduces the
current in the circuit
when it is connected
in series.

GEORG SIMON OHM

Ohm’s law is named after the German
physicist Georg Simon Ohm (1787-
1854). The symbols used in Ohm’s
law are V for volts, R for resistance,
measured in ohms (£2), and I for
the current, measured in amps.
Ohm’s law is used to calculate each
of the above in electrical circuits.
The form V=IR is used to work out
the voltage; I=V/R is used to calculate
the current; and R=V/I the resistance.

Parallel-connected pairs of series-
connected bulbs. All bulbs are
identical, so the current flowing
through each bulb is the same.

CIRCUIT DIAGRAM
The components in a circuit are
shown using a particular symbol for
each one. This is so that the
components and the connections
can be shown in a very clear way. In
this diagram, some of the wires
have been rearranged to make the
diagram simpler, but this would not
affect the way the circuit works.

Switch on a torch: you have just

completed a simple circuit. Electricity flows
from the battery, through the switch and
the bulb, and back to the battery. A
circuit is the path electricity takes as it
flows. All the parts of a simple circuit
must conduct electricity and must be
connected to each other. There are two
main types of circuit: series and parallel.

The torch is an example of a series circuit,
where all the components are connected one
after another. Parallel circuits have batteries or
other components connected across one
another. In both series and parallel circuits
voltages, resistances, or currents passing
through can be calculated by using a
formula called Ohm’s law.

PRACTICAL CIRCUIT

In this circuit, three 4.5-volt batteries connected in
series provide a 13.5-volt supply. If a fault causes too
much current to flow, the fuse will blow and cut off
the supply from the batteries. One of the
multimeters is used as an ammeter to measure the
current flowing through a single bulb. The other
multimeter is used as a voltmeter to measure the
voltage across another bulb.

Three 4.5-volt
batteries connected
in series give an
e.m.f. of 13.5 volts.

Fuseholder contains a cartridge
fuse. A spare fuse is shown at the jj
side. The metal in the fuse melts
if a fault causes a large increase

in the current flowing. »

Connection

point

152

ELECTRICITY AND MAGNETISM

Series and parallel circuits

An electric current flows around a complete
circuit without any gaps. This circuit may
have sections or individual components 1
connected in series or parallel. A circuit
connected in series contains components
attached to each other, like holding hands
in a circle. Components connected in a
parallel circuit are connected
across each other.

£ The fairy lights are all connected
to each other along half of the
length of a wire. The rest of the
wire doubles back to complete
the circuit via the plug and supply.

SERIES CONNECTIONS

£||| When resistors are connected in series, the total resistance is increased.

The current that flows when many resistors are connected across an
electricity supply is lower than when just one of the resistors is used.

Some sets of party lights have many bulbs connected in series.

If one bulb f ails, they all fail.

PARALLEL CONNECTIONS
When resistors are connected in
parallel, the total resistance is
lowered. So the current that
flows increases. Dodgem cars at
a fairground are connected in
parallel. As the number of cars in use
increases, their combined resistance
decreases, and the total current taken
from the supply increases. All the cars
are independent, so if one fails, the
others keep on working.

RESISTANCE

The greater the resistance in a circuit, the less
current that flows. A variable resistor is able to
control the amount of current that flows
through a circuit. This lamp dimmer uses a
variable resistor, made of graphite pencil
lead, to alter the brightness of a bulb. A
movable sliding contact alters the amount of
carbon that the current has to flow through.
Increasing the length of carbon in the circuit
increases the resistance, reduces the current,
and dims the bulb. Large variable resistors
used in this way are called rheostats.

Battery

A large current flows
when there is little
resistance, so the
bulb glows brightly.

Carbon track

VOLUME CONTROL
The volume control in a typical
radio is a variable resistor. It has a
contact that slides over a carbon track
when the control is adjusted. An electrical signal is
applied across the resistor. By adjusting the setting, all
or just a part of this signal can be used to make sound.
This sort of variable resistor is called a potentiometer.
Contact

Only a small current
flows when the
resistance is higher, so
the bulb is dimmed.

Connections
to track

Contact slides
over resistor
when trigger
squeezed. ^

ANDRE-MARIE AMPERE

The French mathematician
and scientist Andre Ampere
(1775-1836) carried out
important experiments on
electric currents. His work
enabled people to measure the
amount of electric current
^ flowing through a circuit. In

recognition of his contribution, the
current is measured in units called amperes, or
amps for short. One amp is a flow of about 6
million million million electrons per second.

SPEED CONTROL
Some electric model
racing car sets have a
hand-held unit to
control the speed
of each car. When you
squeeze the trigger, a
contact slides along a
variable resistor that is
connected in series with
a power supply and one
of the cars. As the
resistance is lowered,
the electric current
through the car
motor is increased, and
so the car speeds up.

Find out more

CURI

Ele<

tENT ELECTRICITY I

CTROMAGNETISM P.

Tectricity IN thi
HOME P.161
Fact finder p.410

>.148

.156

ELECTRICITY AND MAGNETISM

Magnetism

A MAGNET IS NOT STICKY, and yet objects made of
iron or steel cling to it. A magnet is surrounded by an
invisible field of force (its magnetic field) that
affects certain materials nearby. All magnets have
a south pole and a north pole; north poles are
always attracted to south poles. When you think
of a magnet, you probably picture a permanent
magnet (one that keeps its magnetic power).

But an ordinary piece of iron becomes
magnetized when it is near a magnet, gaining
a north and south pole. The first use of
magnetism was in the magnetic
compass. Today, magnetism is
used in many other ways.

Earth’s magnetism

The region around any
magnet, where its magnetism
can be detected, is called a
magnetic field. The Earth has
a magnetic field, just as if a
permanent bar magnet is inside
it. The field is caused by the iron
core at the centre of the Earth.

Each individual iron filing
has been turned into a tiny
magnet. They align with
the big magnet's field.

JPW magnet

Iron filings around a
bar magnet always arrange themselves into the
same kind of pattern. They make the magnetic
field around the magnet show up. The lines
show the direction in which a compass needle
would point when placed near the magnet. The
Earth’s magnetic field has little effect on the
compass, because it is so close to the bar magnet.

AURORA

The Earth’s magnetic poles attract charged
particles emitted by the Sun. When these particles
'Strike gas particles in the atmosphere, coloured
light is radiated. In the Northern Hemisphere, the
display of light, seen here in Alaska, U.S.A., is
called aurora borealis, meaning “northern dawn”.

It is also called the northern lights.

MAGNETIC COMPASS
A pivoted magnet will line itself up in a
north-south direction, because of the
Earth’s magnetic field. This effect is used in
the magnetic compass. But navigators must
allow for the fact that a compass will point to
the Earth’s magnetic north, which is not quite
the same as the geographical north.

POLES

Magnets show both attractive
and repulsive forces. Every
magnet has a north and a
south pole, named according
to which geographic Pole of
the Earth they are attracted
towards; opposite poles
attract and like poles repel.

A north pole of a compass
points north because the
Northern Hemisphere has a
south magnetic pole. Iron
filings can reveal attractive
and repulsive forces
between magnets.

South

pole

North
pole

Iron filings reveal the repulsive
forces between like poles.

South

pole

South

pole

North i ron filings reveal South North

pole the attractive force P ole P ole

between unlike poles.

SOLAR PROMINENCE
Using special telescopes,
astronomers can photograph
glowing streams of hydrogen
gas hundreds of thousands of
kilometres above the Sun’s
surface. These are called
prominences. The gas
contains moving charged
particles, which are affected by
the Sun’s powerful magnetism.
The enormous prominence
shown here is being held up
by magnetic forces.

154

ELECTRICITY AND MAGNETISM

What makes a magnet?

Inside a piece of steel are large numbers of tiny
magnetized regions called domains. These are usually
jumbled up, so their effects cancel out, and the steel is
not magnetized. If the domains point in the same
direction, the steel becomes a magnet. The end that the
north poles of the domains point towards becomes a
north pole, and the other end is a south pole.

MAGNETIC
CIRCUITS

A magnet gradually loses its
magnetism if it is stored by itself.

The domains may gradually shift
position (especially if
the magnet gets hot
or is shaken), so they
are no longer lined up.

To stop this happening,
piece of iron called a keeper
is placed across the poles of a
horseshoe magnet. Domains in
the keeper are pulled into line by
the magnet; domains in the magnet
are kept in line by the keeper. This
arrangement of domains is called a
magnetic circuit; it prevents the magnet
from losing its magnetism.

MAGNETIC TAPE

A cassette tape contains a plastic tape with a
coating of iron oxide or chromium dioxide.
Magnetic patterns can be applied to the tape
by the head of a tape recorder. This changes
electrical sound signals into a changing
magnetic field, which induces patterns of
magnetism on the tape. On replay, this
magnetized tape causes or induces
electrical signals in the head. These are
reproduced as sound.

Recording arranges the domains _
into patterns. These match
the patterns of the
sound signal.

In unmagnetized steel, the
magnetic domains are
jumbled. Their north and
south poles cancel each
other out.

The domains
in the magnet
are lined up
in relation to
each other.

Stroking steel with a bar magnet
magnetizes the steel. The
magnet pulls the domains in the
same direction.

REFRIGERATOR MAGNET
A refrigerator magnet can hold a
piece of paper to a fridge door,
showing that magnetism can act
through a non-magnetic solid. The
fridge door acts like a keeper when
a toy magnet clings to it. A
magnetic circuit is set up between
the refrigerator and the magnet;
this preserves the magnetism
of the magnet.

Striking a magnet with a hammer
shakes up the domains. Their
like poles push apart and the
steel loses its magnetism.

Sound signals

Twin-track
electromagnetic
record/playback head

Tape erased by high-frequency
alternating magnetic field. The
inaudible high-frequency signal
replaces any previously recorded
sound signals on the tape.

BURGLAR ALARM
A permanent magnet is mounted
on the door, and a reed switch is
mounted on the frame. When the
door is closed, the magnet makes
the two upper magnetic iron
strips cling together. When the
door is opened, the magnet
moves away and the centre strip
springs back. It touches the non¬
magnetic contact below,
completing the circuit and
activating the alarm.

MAGNETIG
DISKS

Computers store
data on plastic disks
that have a coating that
can be magnetized. As in
a tape recorder, the material
to be recorded is in the form
of electrical signals. The disk is
spun, and a recording head passes
over its surface. This head changes
the electrical signals into magnetic
pulses, leaving the information stored
on the disk as magnetic patterns.

The hard disk drive unit
contains a stack of hard
(rigid) magnetic disks with
their own read/write heads.

Reed switch with iron
reed, unconnected
iron contact (top),
and non-magnetic
contact (bottom).

Electromagnetic read/write head,
under computer control, moves to
an unused part of the disk for
writing (recording) information, or to
a previously written section that is
to be read (retrieved) from the disk.

Permanent magnet on door
makes iron reed stick to
unconnected iron contact
when door is closed.

Find out more

Transition metals p.36
Electromagnetism p.156
Electric motors p.158
Generators p. 159
Structure of the
earth P.212
Sun p.284
Fact finder? A\0

155

ELECTRICITY AND MAGNETISM

Electromagnetism

Many THINGS AROUND YOU, such as electric
bells, motors, and loudspeakers, use electricity
to make magnetism. An electric current will
always produce a magnetic field. Magnetism
made in this way is called electromagnetism; a
magnet created in this way is called an
electromagnet. Permanent magnets do not need
electricity, so why would anyone want to use a
magnet that works only when a current passes
through it? In fact, electromagnets can do many
things that permanent magnets cannot. You can
switch an electromagnet on and off, so that it
works only when you want it to. Also, changing
the strength of the current alters the strength of
the magnetism. This effect is
used in loudspeakers.

The amount of current passing
through the
is automatically
to keep the train
hovering at the
right height.

The latch is drawn into
the coil when a current
passes through it.

Door iatch

You can unlatch your front door from
elsewhere using an electromagnetic door latch.
This has a coil called a solenoid. Pressing a switch
inside the house makes a current flow through the
solenoid. The magnetism produced pulls an iron
latch into the solenoid so that a caller can open
the door. A spring returns
the latch afterwards.

Bell

DOORBELL

One use of electromagnetism is in
an electric doorbell. When a visitor
rings, a current flows through the
electromagnet. An iron bar linked
to a hammer is attracted by the
magnetic field, and the bell is
struck. The circuit is now broken,
the magnet is switched off, and the
iron bar springs back. The whole
process repeats rapidly to make a
continuous ringing sound.

Hammer

Iron bar

\ • Solenoid
; which

becomes
***& magnetic
the

current flows
through.

HANS CHRISTIAN
OERSTED

In 1820, Danish
physics professor
Hans Christian
Oersted (1777-
1851) was doing
experiments with
some electrical
equipment. He saw that
when he passed a strong electric
current through a wire, a nearby
compass needle deflected so that it
no longer pointed to the north.
Oersted realized the electric current
was producing magnetism, and that
this disturbed the needle. He had
discovered electromagnetism.

FIELD AROUND A MIRE
Around a wire carrying an electric
current is a magnetic field. It can
be detected using iron filings or a
magnetic compass.

FIELD AROUND A COIL
The magnetic fields around the
wires combine to form a stronger
field. Like a bar magnet, the coil
has a north pole and a south pole.

Before pressing the
button to open an
electromagnetic door
latch, you first speak to
the caller on an intercom
to check who is there.

Attached to the sides of the track are
rails containing electromagnets. The
train’s electromagnets pull towards them.

MAGNETIC LEVITATION
Magnetic levitation (maglev) trains give a veiy smooth
and quiet ride. These do not run on rails but “float” above
them by using electromagnetism. A current passes through
electromagnets in the track and on the train. The
magnetism produced lif ts the train upwards.

Every electric
current produces
a magnetic field.
If the current is
moving away
from you, the
direction of the
field is
clockwise.

When a current flows
through a coil (wire
wound round and
round), the magnetic
field produced is like
that of a bar magnet.

156

ELECTRICITY AJNI) MAGNETISM

A coil of fine,
insulated
copper wire
wound on an
iron nail

Electromagnet

Winding an electromagnet
around an iron core increases
the strength of the magnetic
field produced. For example, if
many turns of copper wire are
wound around an iron nail, a
strong electromagnet is made. The
copper wire must be insulated so
that the current cannot bypass any
turns. When connected to a torch
battery, this electromagnet
will pick up small iron
and steel objects.

While a battery is connected to
the coil, the nail becomes
magnetized and can pick up steel
paper clips and drawing pins.

EYE SURGERY
A surgeon may use an
electromagnet to remove
a steel splinter from a
person’s eye. Once the
electromagnet is in the
right place, a current is
passed through it. The
powerful magnetism pulls
the metal from the eye.

The vibrations of
the cone send
sound signals
through the air.

A doctor can remove a splinter
much more cleanly using an
electromagnet than he or she
could do by hand.

CAR FUEL GAUGE

Electromagnetism can tell car drivers how much
petrol they have lef t. An electromagnet sits inside
a permanent magnet. A current flows through the
electromagnet, which then turns towards the
permanent magnet. The amount it turns depends
on the strength of the current. Inside the petrol
tank, a float moves a variable
resistor to control the current
flowing through the fuel meter.

When the fuel level is high, a high
current flows, causing a large
deflection of the pointer.

VENDING MACHINE

As well as electricity making magnetism, magnetism
can make electricity too. This is used by vending
machines to recognize coins. The coin passes through
a magnetic field. This sets up an electric current in
the coin, called an eddy current. This in turn
produces a magnetic field which slows the coin down.
Genuine coins are slowed
by just the right amount
to fall into the next part
of the machine. Other
coins fall into a
reject chute.

Coins inserted into
machine

Some coins of the
wrong metal slow
down too much /
and fall into /
reject chute.

Coins of correct
metal slow just enough to
pass over the reject chute
into the next part of the coin¬
checking mechanism.

Non-metallic objects
are not slowed down,
so they hit the upper
plate and fall into
reject chute.

Coil of wire, through which a
changing current flows

This vending machine
uses electromagnetism to
recognize the right coins.

LOUDSPEAKER
A loudspeaker changes electrical
signals into sound waves. The
signals pass through a coil which
is wound around the neck of a
paper cone. This coil acts as an
electromagnet. Nearby is a strong
permanent magnet. When the
current flows one way, the
magnetic forces push the
electromagnet and the cone
outwards. When the current flows
the other way, the cone is pulled
inwards. The vibrations of the
cone form sound waves.

Powerful permanent
magnet

A float adjusts
the setting of a
variable resistor.

Battery

The current
magnetizes the
coil, causing the
pointer to move.

South
pole

Permanent

magnet

METAL DETECTOR
In an airport, you may have to walk
though a metal detecting arch on your
way to the plane. Inside the arch are
large coils of wire carrying an electric
current. If a person goes through the
arch with a gun concealed in their
pocket, the metal in the gun alters the
electromagnetism produced by the
coils. This change can
be detected and an
alarm will sound.

Find out more

CURI

IENT ELECTRICITY 1

Magnetism p.154
Sound p. 178

Fa ct finder p . 410

3 .148

157

ELECTRICITY AND MAGNETISM

The thuMb gives
the direction of
Motion of the wire.

Electric motors

Magnetic field Coil

The First finger
shows the
direction of the
magnetic Field.

The seCond
finger shows
the direction
f the
conventional
electric
Current.

LEFT-HAND RULE
You can work out which way
a wire carrying a current will
move through a magnetic
field by using a rule called
Fleming’s left-hand rule.
Hold your lef t hand as
shown, with the two fingers
and thumb all at right
angles to each other.

Permanent
magnet
(north pole)

Many of the machines that we use every day

are powered by an electric motor. Such a motor
changes electricity into movement. It makes use of
the fact that a wire carrying a current produces a
magnetic field and so will feel a force in another
magnetic field. This force can produce movement.
Electric motors are convenient sources of power
because they are clean, fairly quiet, and very versatile.
Washing machines, food mixers, video recorders, and
record players have electric motors that make them
work. Cars use electric motors to start up and to
operate windscreen wipers. But few cars run on
electric motors because batteries of a reasonable
size cannot store enough energy to power a
modern car for long journeys.

k w w Battery

1. Current flows through w w ^

the coil, and the field of the
permanent magnet forces the
right side of the coil down and the left side up, in
accordance with Fleming’s left-hand rule.

Simple motor

In a simple electric
motor, direct current is fed into a
coil by carbon rods called brushes.
The coil sits between the north and
south poles of a permanent magnet.
The magnetic fields of the coil and
the permanent magnet interact,
forcing the coil to turn. To keep up
the rotation, the current is reversed
every half-turn by an attachment
called a commutator. The
continuous turning motion of the
coil drives the motor.

2. The coil
continues
turning towards
the vertical, and its inertia will
carry it beyond this position.

JOSEPH HENRY
American physicistjoseph Henry
(1797-1878) made many important
discoveries about electromagnetism.

He improved the design of
electromagnets, and in 1829 he
built the first useful
electric motor.

This used
electromagnets
to make a
pivoted beam
rock up
and down.

3. On passing
the vertical, the
commutator reverses
the connections to the
brushes and, therefore,
also reverses the current in the coil. So the
side that was moving up now moves down.

4. The coil
continues spinning,
and here its inertia is
about to carry it past the

vertical position again. The resultant reversal of current
each half turn causes the coil to spin continuously.

Wheels of

model locomotive pick up
electricity supply from the rails.

MODEL TRAIN

An electric motor drives this model
locomotive. It picks up electricity from the
tracks through its wheels. Wires connect
the wheels to the metal strips which touch
the motor’s commutator. A control unit
can vary the voltage supplied to the tracks.
The higher the voltage, the stronger the
magnetic field made by the coils in the
motor. This means the motor turns faster,
so the locomotive speeds up.

Metal strips (brushes)
connect the electricity
supply from the rails to
the commutator of
the motor.

The coils, wound on
iron cores, act as
electromagnets.
They are connected
to the commutator
of the motor.

Low-voltage
direct current
supply to the rails

Permanent
magnet produces
the magnetic
field in which the
coils rotate.

The commutator picks up electricity from
the brushes. The commutator makes the
coils carry on turning in the right direction.

MULTIPOLE MOTORS

In a simple motor, the turning
force on a coil carrying a current
is greatest when the windings
are in line with the magnetic
i field, and weakest when the
windings are at right angles to
the field. Most electric motors
have several coils to give a
smoother turning force. Current
is supplied to the coils by a
commutator with many sections.

Find out more

For

CURl

Elf.i

CES AND MOTION P

Engines p.143

IE NT ELECTRICITY I

CTROMAGNETISM P

Fact finmer p.410

.120

>.148

.156

158

ELECTRICITY AND MAGNETISM

Generators

The thuMb shows
the direction of
Motion.

Everyday, WE USE ELECTRICITY made by powerful machines
called generators. These work in the opposite way to electric
motors; they turn movement into electricity. The principle they
work on is called electromagnetic induction: electricity is
produced in a wire when it moves in a magnetic field, or when a
nearby magnetic field moves or changes in strength. Large
generators are used in power stations to produce
the mains supply that we take for granted in
our homes. The movement is given by
steam, moving water, or wind. Small
generators called dynamos are used
on bicycles to power the lights.

Bicycle d\namo

One type of bicycle dynamo has a
small wheel touching the rear
tyre of the bike. When the bike
moves, the wheel turns; this
movement makes a
permanent magnet spin
near a coil that is wound
on an iron core. The wires
in the coil experience a
changing magnetic field
from the spinning magnet,
so electricity is generated in
them. This effect is called
electromagnetic induction - a
voltage is induced in the coil.

The First finger
shows the
direction of the
magnetic Field.

The seCond
finger gives the
direction the
Current will flow.

RIGHT-HAND RULE
A rule called Fleming’s right-hand rule can
show the direction in which current will
flow in a wire when the wire moves in a
magnetic field. Hold your right-hand
thumb, first finger, and second finger at
right-angles to one another.

Coil

Permanent magnet
(south pole) ^

DIRECT CURRENT GENERATOR
In this direct current generator, a
coil of wire is turned between
the poles of a permanent
magnet. The direction of
the current in the coil
reverses every half¬
turn, because
each side of the coil
alternately passes up and down
through the magnetic field. But the
current that passes through the bulb
flows in one direction only, because
the commutator changes the
connections every half turn.

North
pole

Commutator

ALTERNATOR

A generator that produces alternating current
is called an alternator. In this simple version, a
coil of wire is spun between the poles of a
permanent magnet. This creates a current in the
wire that is carried to the lamp by carbon
rods called brushes. The current through
the coil and bulb continually alternates
(changes direction); the current
through the bulb is alternating too. Djrect currenl is produced in pulses

that flow in one direction only.

Alternating current is produced in
waves that flow first in one direction,
then in the opposite direction.

MICHAEL FARADAY

Michael Faraday (1791-1867)
was the son of an English
blacksmith. He started
I work as a bookbinder.

Inspired by the science books
he bound, he took up physics and went on
to make many discoveries. In 1821, he
found that electricity could produce rotary
motion; today’s electric motors are based on
this. In 1831, he showed that relative movement between a
magnet and a coil of wire could induce electricity in the
coil - an idea that gave birth to modern generators.

mmm

MOVING COIL MICROPHONE
A microphone generates electric
signals from sounds. In a moving coil
microphone, sound waves strike a
diaphragm and vibrate a coil which is
positioned between the poles of a
permanent magnet. The voltage induced in
the coil varies in strength and frequency in
the same way as the sound waves.

Find out more

Nuclear energy p. 136
Engines p.143
Electromagnetism p. 156
Making and hearing
sound P.182
Electromagnetic
spectrum P.192

159

ELECTRICITY AND MAGNETISM

Electricity supply

HOW CAN THE WALL SOCKETS in your home supply you
with electricity? Because they are connected to power stations.
In a power station, a turbine is driven by steam power (or
water or wind power). The turbine then drives an electricity
generator. So the generator converts kinetic energy (the
movement of the turbine) into electrical energy. Most
generators produce an alternating supply of electricity and
are called alternators. Alternating current (a.c.) is more
convenient than direct current (d.c.) because
it can be changed to a higher or lower voltage by a device
called a transformer. So the different voltages needed can be
supplied to factories, offices, stores, and homes.

POWER PYLONS
The cheapest way to run
cables across the country is
to suspend them from
towers called pylons.
I nsulators between the
cables and the supports
prevent the current
from leaking away
through the pylons. In
towns, the cables are
usually underground.

For heavy industry, the
voltage is reduced from
132,000 volts to
33,000 volts.

At the power station, steam turns
a turbine linked to an electricity
generator. The output of the
generator is at 22,000 volts a.c.

A step-up transformer changes
the generator output of22,000
volts to 400,000 volts for
feeding the grid system.

The grid system carries
the 400,000-volt supply
around the country.

At a substation the
voltage is reduced from
400,000 volts to
132,000 volts for
local distribution.

For light industries,
the voltage is reduced from
33,000 volts to 11,000 volts.

Power supply

Power stations send electricity through long cables to homes, offices, shops,
railways, farms, and factories. The same power can be sent at low voltage and
high current, or at high voltage and low current. Resistance in the cables causes
some power to be wasted as heat, but much less power is wasted at low current. So
the electricity from a power station is supplied at a high voltage, so that the current,
and power losses, are reduced. Transformers reduce the voltage in stages to provide

iron core the supplies required by various consumers.

Primary

fc NIKOLA TESLA

^In 1887, the American
[ inventor Nikola Tesla
j (1856-1943) patented a
^generating and distribution
r system that transmitted
r alternating current. It won
over his former boss Thomas
Edison’s direct current system.
The two men were to have been
awarded a joint Nobel Prize in 1912. But
Tesla refused to have anything to do with
Edison, and neither man received the prize.

Secondary Primary

A step-down
transformer
has fewer
coils in the
secondary
coil.

TRANSFORMERS

The high voltages from power cables need to be
converted into levels that we can use in our
homes. Transformers do this job. A simple
transformer consists of two coils wound onto the
same iron core. When an alternating voltage is
applied to one coil (called the primary coil), it
produces a changing magnetic field in the core.
This induces an alternating voltage in the other
coil (called the secondary coil).

Secondary

A step-up
transformer
has more
coils in the
secondary
coil.

Find out more

Poor metals p.38
Work and Energy p. 132
Energy sources p. 134
Cells and batteries p.150
Generators p.159
Fact finder? AH)

160

ELECTRICITY AND MAGNETISM

Electricity in the home

With ELECTRICITY READILY AVAILABLE at the flick of a
switch, it is easy to forget how much we depend on it. The
electricity supply runs our homes. This electricity has
travelled from far-away power stations. When there is a
power failure, we realize how many devices in the home
depend on this supply. The lights go out, and suddenly you
have to search for candles. The television no longer works -
you have to listen to a battery-operated radio instead.

Electric heaters, cookers, dishwashers, washing machines,
dryers, and many other appliances can no longer be used.

Light bulb

Most electric light bulbs
have a thin tungsten wire
called a filament, mounted
in a sealed glass bulb. When
a current flows through, the
filament glows white hot. The
wire takes some time to burn
out because most of the oxygen
(needed for burning) has been
removed from the bulb.

Domestic circuits

The electricity supply coming into our
homes first passes through main
fuses. It then reaches a meter that
measures how much electricity we
use. A consumer unit is connected
to the other side of the meter.

This contains fuses or circuit
breakers to protect the
house circuits.

The consumer unit -

contains fuses or circuit
breakers that feed
various circuits in the
house. Units designed
to take fuses only are
called fuse boxes.

The electricity meter
measures how
much energy the
consumer uses.

The incoming 110-
or 220-240-volt
mains supply first
passes through
heavy-duty fuses.

All the ceiling lights
are run from a circuit
that runs between
the ceiling fittings.

An electric
cooker
takes a lot
of current,
so it has its
own circuit.

All the wall sockets on one floor of
the house are connected across a
looped circuit called a ring main.

Various
appliances are
plugged into the
wall sockets.

PLUGS AND
SOCKETS
Electrical appliances
need to be connected to
the electricity supply. This
is usually done via plugs on
the appliance which fit into
sockets leading to the supply.
Different countries use different
wiring colour codes.

IEPH

%o \

CIRCUIT PROTECTION

Electricity can accidentally cause a fire by heating a wire so
much that it becomes red hot. This usually happens when a
fault causes too much current to flow. To prevent this from
happenings domestic circuits are protected by devices called
fuses and circuit breakers. Both cutoff the current if it
increases to a dangerous level.

POWER AND ENERGY
Power, the rate of using energy, is
measured in watts. When electricity
flows through a resistor, the power
equals the voltage multiplied by the
current. A 240-volt cooker ring, taking
a current of 4 amps, has a power of
960 watts. We can work out the total
energy consumed by multiplying the
power by the time that the ring is on;
in two hours, the ring consumes
2 x 960 = 1920 watt-hours, or 1.92
kilowatt-hours (kWh) of electricity.

The simplest mains supply
systems use two wires, and
therefore need only two-pin
plugs and sockets.

Many mains supply systems
have a third wire, the earth wire.
It is connected to a metal rod in
the ground, and ensures that
exposed metal parts can never
become live and cause shocks.

Some plugs have a fuse. If
an appliance takes too much
current, the fuse in the plug
blows, rather than a fuse or a
circuit breaker in the consumer
unit. So power is still available
at all the other sockets.

Earth wire

Fuse

■mm

This wire melts to
break the circuit.

A circuit breaker is an
electromagnetic switch that cuts off
the current when it becomes too high.

A fuse is an enclosed length of wire that
forms the weakest link in a circuit. It
bums out safely to cut off the current
when this becomes too high. Fuses are
available to withstand various currents.

Find out more

Work .and energy p. 132
Current electricity p. 148
Cells and batteries p. 150
Circuits p.152
Sources of light p.193
Fact finder p.410

161

ELECTRICITY AND MAGNETISM

Telecommunications

The WONDER OF TALKING to someone who is
thousands of miles away is only possible because of
electricity. Electronic equipment converts sounds
and pictures into electricity, which then travels with
lightning speed to somewhere else to be
changed back into sounds and pictures by
other electrically powered equipment. A
huge amount of information, from fax
messages to telephone conversations, travels
back and forth through telephone lines.
Information can also be transmitted as light in
fibreoptic cables or as radio waves, which are sent
up to a satellite high up in space to be
retransmitted to a receiving dish. Computers and
other electronic machines can communicate with
each other via telephone lines. All these forms of
communication need three things: a transmitter to
send out the information, something to carry the
signals, and a receiver to convert signals back into a

form that we can understand.

TELEGRAPHIC RECEIVER
In the 1830s, Samuel Morse invented a
printer to record messages sent on his electric
telegraph. A strip of plain paper moved slowly through
the machine. Each pulse of current received made an
electromagnet move an inked wheel, so that the dots and
dashes of the Morse code were printed on the paper strip.
Operators used a switch called a Morse key to send signals.
Pressing the key allowed electricity to flow, which activated
the inker (or a clicker) at the other end. Messages were
received as they were being sent.

Inker

Morse key

Morse code is sent as a
combination of dots, dashes, and
spaces that represent numbers
and letters of the alphabet. Here
the numbers 4 and 2 have been
printed out.

• • • •

• •

Four dots and a dash represent 4.

Two dots and three dashes represent 2.

Telephone

When you dial or push buttons on a telephone, a series of
dialling signals is sent out. These signals make automatic
equipment connect your call. The bell or bleeper at the other
end then sounds. When you speak, the microphone in the
handset turns your speech into electrical signals, which are
sent to the person at the other end of the line. Their receiver
turns the incoming speech signals back into sounds.

Diaphragm

Electromagnet

DIALLING
Dialling signals are either simple
electrical pulses or mixtures of tones
(musical notes). Electronic equipment
at telephone exchanges counts the
pulses or recognizes the tones so that it
can make the right connections.

When you dial one digit of a number,
switches in the dial send pulses
along the line.

Some push-button phones send out
mixtures of tones. A different combination
is sent by each button. You can hear
these when you press each button.

VIDEOPHONE

Telephones that allow callers to see
each other are called videophones.
Few telephone networks can
transmit information
fast enough to carry a
video signal as well
as a voice signal.

For this reason,
videophones are
still uncommon
in most countries.

A liquid crystal
display (LCD)
screen allows
callers to see

RECEIVER

The receiver in the handset turns
the incoming electrical signal into
sound. The signal passes through
an electromagnet, which attracts a
thin iron disc called a diaphragm.

As the strength of the signal varies,
so the pull on the disc varies, and this
makes it vibrate. The vibrations pass
through the air as sound waves,
which you hear as speech.

Diaphragm

MICROPHONE
Many telephones have a carbon
microphone, also called a transmitter,
which converts what you say into electric
signals. Inside, there is a capsule containing
granules of carbon. When you speak, the
sound waves vibrate a plastic diaphragm.
This pushes on the granules. Every time
they are pushed together, their
resistance decreases. So a current
passed through them varies in the
same way as the sounds causing the
vibrations. This varying current forms
the sound signal that travels to the
receiver in another phone.

162

ELECTRICITY AND MAGNETISM

Find out more

Cells and batteries p.150
Computers p.173
Sound and light p.177
Refraction p.196
Satellites p.300
Factfinder p.410

ALEXANDER GRAHAM BELL

In 1876, Scottish-born American
inventor and teacher Alexander
Graham Bell (1847-1922)
invented the telephone. Bell gave
music lessons, taught deaf people
how to speak, and studied how
sounds are emitted by vibrating
objects. He invented a form of
electric telegraph that sent signals
as musical notes
made by vibrating
reeds. This idea
led Bell to devise
away of sending
and receiving
the frequencies
present in the
human voice.

The result was
the telephone.

SATELLITES
("alls sent via
communications
satellites, which are in
orbit around the
Earth, are transmitted
by radio f rom huge
dish-shaped aerials on
the ground. The
satellite, powered by
solar cells, beams the
signals back to an
aerial in another part
of the world.

Have you noticed a slight
delay when talking to someone
on an overseas call? This can
be because the call is going
via a satellite. Radio signals
take a little time to travel to
and from the satellite.

Communications links

Communications When y ou make a call > the dialling pulses
satellite pass along wires to your local telephone

exchange. Equipment there recognizes the
codes in the pulses. For a local call, the local
exchange connects you. For a different area,
you are connected with the exchange in that
area. Equipment there then makes the
connection to the number you want.
International calls are sent through
international exchanges. The
whole system of connecting
links is called a network.

Sending and
receiving dish

The wires from your
telephone at home go, with
similar wires from other
homes, to the local
exchange.

Local exchange

Local
exchange

SATELLITE STATIONS
A satellite telecommunications station
has a large dish-shaped aerial pointing
at the satellite. Electronic equipment
connected to the aerial amplifies the
signals transmitted and received. Such
stations are connected to local
telephone exchanges.

Sending and receiving
satellite communications dish

This dish receives radio waves
from the satellite and sends
the information on to
the exchange.

International

exchange

Cellular communications
exchange

International

exchange

EXCHANGES

Exchanges covering different areas
are linked together, by cables,
microwave links, or satellite systems.
Such links enable people in one area
to contact people in other areas.

Microwave transmitting and
receiving aerials are placed on tall
towers or buildings and carefully
lined up with each other.

MICROWAVE LINKS

Microwave links use radio waves called microwaves to
carry telephone and other signals. Microwaves travel in
a straight line f rom a dish¬
shaped transmitting aerial
to a similar receiving aerial.

FAX

Fax machines use the
telephone network to send
written or printed material. The
sending machine changes the
images on the document into a

code of electrical signals and sends them down
the telephone line. The receiving machine uses
these to reproduce the original document.

Local

exchange

A fax machine
both sends and
receives letters
and other
documents.

Microwave

communi¬

cations

tower

A local
exchange
connects local
calls, and
routes other
calls to other
exchanges.

Portable telephones

People driving along can talk to each
other using portable telephones with
built-in radio transmitters and receivers.
A low-power transmitter in the
telephone connects the call to
permanent receiving equipment
installed in the area, called a cell. From
there, the call is connected into the
telephone network. A local transmitter
sends incoming signals to a radio
receiver in the telephone. The whole
system is called a cellular network.

Cell

Local transmitter

163

ELECTRICITY AND MAGNETISM

Wavelength is longer
at low frequencies. It
can be measured from
one peak to another.

Long wave (low frequency)

Radio

Wavelength is shorter
at high frequencies.

/N/X/WW/

Medium waive

Short wave

VHF (very high frequency) UHF (ultra-high frequency)

When you listen to the radio, your set picks out the

station you want from thousands that reach it. Radio signals
travel as invisible waves through the air, other materials, and
even empty space. Radio waves, like light waves, move at about
300,000 km (186,000 miles) per second. The main use of radio
waves is for carrying sounds and pictures for broadcasting and
for private communications. News that once would have taken
months to reach distant parts of the world now gets there in
less than a second by means of radio waves bounced from
communications satellites in space. Radio waves are produced
by a circuit carrying an electric current that rapidly

oscillates (reverses its direction of flow). Radio waves
are sent out most efficientiy by putting the

transmitting aerial on high ground, which
is why many transmitters are on hills.

The carrier starts off with
constant amplitude and
constant frequency.

The sound signal
varies in amplitude
and frequency. N

GUGLIELMO MARCONI

The first person to give a practical
demonstration of radio was Sir
Oliver Lodge. In 1894, he sent
Morse code messages a distance of
55 m (180 ft). At about the same
time, an Italian engineer called
Guglielmo Marconi
(1874-1937) managed
to transmit a message
over two kilometres
(1.25 miles). In
1896, Marconi came
to England where he
established radio as
an important and
practical means
of communication.

An AM radio signal. The strength of the carrier is varied
(modulated), shown by the changing size of the wave.

Modulation

Making radio waves carry
sounds (or other signals)
is called modulation. The sound signal
makes a steady radio signal, called the
carrier, vary in some way. In amplitude
modulation (AM), the amplitude
(strength) of the carrier changes. In
frequency modulation (FM), the
frequency of the carrier changes. FM
transmissions suffer less from crackles
and other interference.

Coil and variable
capacitor form tuned
circuit to select
the required
station.

Wire aerial changes all
received radio waves
— into electrical signals.

An FM radio signal. Here, the frequency
of the radio waves is varied (modulated).

Valve

1 1 i

Capacitor

Transistors

amplification

Some early radio sets had
valves to amplify
(strengthen) the received
signals. Later, sets became
much smaller when
transistors replaced valves.

Earth wire jhe crystal diode and the capacitor
attached detect the sound component of the

to pipe transmitted signal.

CRYSTAL SET

In the 1920s, many people listened to radio broadcasts using
crystal sets. A common type of crystal set had a crystal of
galena (lead sulphide) and a pointed wire contact (called
the cat’s whisker). Together these acted as a diode, which
was used in the set’s detector circuit. The detector extracted
the sound component from the transmitted radio signal.

RADIO

1863 James Clerk Maxwell
suggests a mathematical
description of electromagnetic
waves.

1888 Heinrich Hertz sends
and receives radio waves in his
laboratory.

1896 Guglielmo Marconi
patents the first practical
wireless telegraphy system.

1901 The first telegraph
signal is sent across the
Atlantic.

1906 Reginald Fessenden
makes the first radio
broadcast. This astonishes
wireless telegraph operators,
who hear music instead of the
usual Morse code.

164

ELECTRICITY AND MAGNETISM

Radio transmitter

In a radio transmitter, a circuit
called an oscillator generates a
rapidly alternating voltage called the
carrier signal. This passes into another
circuit called the modulator. The sound
signal from the radio studio is fed into
the modulator too. In the FM transmitter
shown here, the sound signal modulates
(varies) the frequency of the carrier
signal. An amplifier strengthens the
modulated carrier signal. The
strengthened signal is then radiated
as radio waves from a transmitting aerial.

SOUND SIGNALS

In a radio studio, a microphone turns
the sound of the voice into an electric
signal. Other equipment forms
sound signals when tapes and
records are played. These
signals can be mixed
together. The combined
signal goes to the transmitter.

The transmitting
aerial radiates the
signal from the
transmitter as
radio waves.

Radio receiver

The aerial of a radio set receives radio waves
from many transmitters. It changes the radio
waves it picks up into tiny electrical signals. These
go to tuning and amplifying circuits. Here, the
signal from the required station is picked out and
strengthened. Then a circuit called a detector
separates the sound signal from the carrier. The
strength of the sound signal is adjusted using the
volume control. The sound signal then goes to an
output stage. This amplifies the signal so that
it is strong enough to work a loudspeaker.
The loudspeaker changes the signal back
into sounds, like those in the radio studio.

Amplification
strengthens the
modulated carrier
before it goes to
the aerial.

The tuning control is a variable
capacitor. It is used to select a station.

The frequency of
the carrier is
modulated by the
sound signal.

The frequency of
the carrier signal is
about 100 million
waves per second
(100 megahertz).

The volume
control is a variable
resistor. It adjusts
the level of the
sound signal.

The output
amplifier sends a
strong current through
the loudspeaker to
reproduce the sound.

Loudspeaker

WALKIE-TALKIES

Portable transmitter-receivers
called walkie-talkies are used on
building sites so that people on
the ground can easily talk to
construction workers at the top of
the building. They are also used
by police all over the world to
help them fight crime.

The receiver and
transmitter in a
walkie-talkie are
battery-powered.

THE IONOSPHERE

From 50 to 400 km (30 to 250 miles) above
the Earth is a region of the atmosphere called
the ionosphere. It contains ions and free
electrons, which make it reflect some radio
waves. This is essential for transmitting low-
f requency radio waves over long distances.

Relatively high-frequency signals pass through
the ionosphere, so they are used to beam
signals via communications satellites
thousands of kilometres above the Earth.

These frequencies are also used for short-
distance overland transmissions.

Short waves are reflected off
the top of the ionosphere.

Relatively low-frequency
(long wavelength)
signals from transmitters
can reach distant
places by repeated
reflections between
the ionosphere
and the ground.

A communications satellite receives
radio signals from one place on the
Earth and retransmits them to another
area. Transatlantic transmissions are
often made in this way.

Some radio waves simply
travel through the air without
needing to be reflected.

Find out more

Generators p.159
Electronic

COMPONENTS P. 1 68

Elec :trom agnetic
SPECTRUM P.192
Telescopes on earth p.297

165

ELECTRICITY AND MAGNETISM

TELEVISION

Transmitter

TELEVISION AFFECTS all our lives. We learn about
places we shall never visit, we see important events as
they take place; some programmes we watch purely
0k for entertainment. Television became popular in the
jK 1950s, but ideas for sending pictures over long distances
E date back to the 19th century. Thanks mainly to inventions
such as valves, transistors, and the cathode-ray tube, we now
W have high-quality television systems. In many countries,

^ television pictures and sound are transmitted nationally using
UHF (ultra-high frequency) radio waves or electrical signals
through cables. Television is also transmitted internationally via
satellites. Closed-circuit television is used for security in banks i
and other buildings; the pictures travel straight from the J

camera to the screen. ™_„JB

I.IVE TELEVISION 11121

When a programme is broadcast live, a television mSNk
camera changes light from the scene into electric

signals. These are transmitted by radio and a

changed back into pictures by the television set. j

TELEVISION STUDIO
Picture signals from the cameras and
sound signals from the microphones go
to a control room overlooking the
studio. There, all the pictures are shown
on screens. The programme director
decides which picture to use and when
to change to another shot.

f The light
enters the
camera through
the first lens.

--Special
mirrors split
the light into
three colours.

Red, blue, and green light
fall on separate tubes.

An amplifier strengthens the
modulated carrier signal. The
strengthened signal is mixed with
another carrier, which is frequency
modulated with the sound signal.

AMPLIFIER

camera, light from the scene passes
through special mirrors that split the am
light into its primary colour
components - red, green, and blue.

Images in these colours are formed on
three camera tubes. The tubes scan the images.

line by line. Each tube then puts out an
^ electric signal that varies with the

| brightness along each line of the image.

The vision signal amplitude
modulates the carrier signal.

MODULATOR

A device called an oscillator
generates a carrier signal, as in
a radio transmitter.

OSCILLATOR

PRESENTATION SUITE
Here, signals from live and recorded
sources are selected and controlled.
The pictures are displayed on
screens called monitors. From the
presentation suite, the sound signal,
and a single vision signal containing
all the colour information, are sent
to the television transmitter. The
vision signal also contains timing
information called synchronizing
pulses. These enable the receiver to
reconstruct the picture correctly.

'Jr* FILM AND TAPE

A cinema film is run through a
telecine machine, which forms
electric signals from the sounds
and pictures recorded on the
film. Programmes recorded on tape
are played back on a videotape machine.
The sound and vision signals from many sources
go to the presentation suite. This is a control
room with an adjoining announcers’ studio.

166

ELECTRICITY AND MAGNETISM

Television receivers

Signals from the television
transmitter travel through the air
at the speed of light. The aerial
connected to a television set
changes these radio waves back
into electric signals. In the
receiver, electronic circuits allow
you to tune in to the television
station you want. In a colour
television, other circuits sort out the
three colour components of the
vision signal. The picture tube uses
these to reproduce the picture in
full colour. A loudspeaker
reproduces the sound signal.

COLOUR
PICTURES
Each electron
beam varies in
strength as it scans
the screen, making
the brightness of
the phosphors
(patches of
chemicals) vary.
The beams thus
“paint” three
colour images on
the screen. These
give the impression
of one image in
full colour.

JOHN LOGIE BAIRD

In 1926, Scottish television pioneer John
Logie Baird (1888-1946) demonstrated
the first television system. He used a
rotating disc with holes in it to transform
light from a scene into lines. A photo¬
electric cell changed brightness
variations into electric signals. In
Baird’s receiver, the signals made a bulb
in brightness. The viewer saw a ~
fuzzy image through holes in
another spinning disc. The
system was soon replaced
by a higher quality fully
electronic system.

Baird's spinning disc was
invented by Paul Nipkow
(1860-1940) in 1884. This
diagram shows how a nine-
hole disc reproduces a
picture when a vision signal
makes the
bulb flicker.

SCREEN

Phosphors cover the television
screen. These glow red, green, or
blue when struck by an electron
beam. Some colour tubes have a
perforated plate called a shadow
mask just behind the screen. The
holes in the mask ensure that each
beam strikes only one kind of
phosphor. So each beam forms an
image of one colour.

Horizontal scanning signal applied to
the top and bottom electromagnets.

SCANNING

In a television receiver, beams of
electrons are moved rapidly across
the screen by pairs of electro¬
magnets called line and field
deflection coils. Changing currents
through the coils produce changing
magnetic fields. These fields deflect
the beams of electrons across and
down the screen.

Screen covered in
microscopic dots
of phosphors

Shadow

mask

INTERI^ACED SCANNING
Each second, 25 or 30 complete
pictures are displayed. All the odd
lines and all the even lines are
shown alternately, making 50 or
60 images per second. Increasing
the image rate like this
reduces flicker.

Find out more

OMIC STRUCTURE p

Radio p.164

LLECTROMAGNETIC
SPECTRUM P.192
Colour p.202
Cinema p.208

.24

ELECTRON GUNS
Devices called electron guns inside the cathode-ray
tube fire beams of electrons at the screen. Colour
tubes have separate beams for each of the three
primary colours. The beams vary in strength
according to the brightness of the colour
components in the original scene.

Each electron gun produces one
colour - red, green, or blue.

Electrons pass as a
beam through electrodes
called anodes to the
positively charged
screen of the tube.

A small electric heatei
heats a surrounding
metal cathode, driving
off electrons.

Electron gun

JL.. An...

Vertical scanning signal
applied to the left and right
electromagnets.

PICTURE SIGNAL
The television aerial picks up
the signal radiated by the
transmitter and changes it into
an electric signal. This passes
down a cable to the receiver.

Synchronizing signals
are fed to the scanning
circuits. These
determine the movement
of the electron beams
over the screen.

Circuits separate the
three colour signals.
These control the
strengths of the three
electron beams.

A tuner selects the station.
Other circuits separate and
strengthen the vision,
synchronizing (sync), and
sound signals.

ELECTRICITY AND MAGNETISM

Electronic components

In a triode valve, the electrodes
are in a glass tube that has
had the air removed from it.

The cathode, heated by a
glowing wire filament, sends
out electrons _

The negative charge on the
grid controls the flow of
electrons to the anode __

The anode attracts electrons
because it is positively
charged and electrons are
negatively charged.

TRIODE VALVE
A component called a triode
valve amplifies (strengthens)
electric signals. It consists of a

cathode and an anode with a wire grid between them. When a
small signal is fed to the grid, the charge on the grid alters, which
causes large changes in the electron flow to the anode. The
signal to the anode is therefore an amplified version of the signal
on the grid. Valves have been replaced in radios by transistors,
which means that much smaller radios, called
transistor radios, can be made.

Electronics AFFECTS OUR LIVES more than any other
branch of technology. Radio and television sets, record players, and
tape recorders were the first popular electronic devices to become
available. They use parts called electronic components to control or
change electric signals in some way. These parts include resistors,
capacitors, transistors, and diodes. Today, many electronic
components have been miniaturized (made tiny) so more and more
devices can use them. Some watches, for example, contain complex
electronic circuits that can tell us the time anywhere in the world.
Electronic components in some cameras set the correct exposure
and automatically focus the lens.

Battery contact

Portable radio

A modern portable radio contains many
different electronic components to carry
out many different jobs. The aerial picks
up the signals from the radio stations.
You can select the station you want
using a tuning circuit consisting of a coil
and a variable capacitor. Components
called transistors amplify these signals.
The volume is controlled by a variable
resistor that adjusts the level of sound
signals fed to the final amplifier and
the loudspeaker.

Variable capacitor (tuning control)

Waveband selector switch (MWA/HF)

Ferrite aerial rod (for medium waves)

Transistors are used to amplify the
signals picked up by the aerial.

Printed circuit board

Telescopic aerial (for
Very High Frequencies)

Light-emitting
diode (LED)

Variable resistor (volume
control) with on/off switch

RECEPTION

The signals sent out by an AM
radio transmitter are radio waves
that vary in amplitude. The aerial
of a radio receiver changes all
received radio waves into matching
electrical signals. A tuning circuit
then selects the signal required.

DETECTION

The signal selected by the tuning
circuit passes to a diode. This
changes the waves into pulses of
electricity, which charge a
capacitor. As it retains most of the
charge between pulses, the signal
across the capacitor is like the
original sound signal.

Shape of sound
signal “carried” by
the radio waves

Electrical copy
of amplitude-
modulated
radio waves

Original sound
signal

Signal pulses
passed by diode

VARIABLE CAPACITOR
When you tune into a station on a radio,
you may use a device called a variable
capacitor. This has one or more sets of
fixed plates and movable plates that can
cross over without touching. The
capacitance (ability to store charge) is
greatest when the plates are
fully crossed over each other.

Changing the capacitance
makes the radio select different
f requency signals.

Flesistors are used to control
the amount of current in the
circuit. A resistor with a high
resistance value passes a
relatively small current.

Diodes are used
to change the
alternating signals
into pulses of direct
current. This enables
the sound signal to
be re-formed.

Headphone socket

The capacitor changes
pulses of direct current
from the detector into a
smooth sound signal by
keeping hold of the
charge between pulses.

168

ELECTRICITY AND MAGNETISM

The circuit in a
flash unit includes a capacitor
that can hold an electric charge. When
this charge is released to a special
tube, a bright flash is produced.

CAPACITORS

Capacitors are devices that can
store an electric charge and release
it when needed. They are made
from two layers of metal separated
by a layer of non-conducting
material, such as plastic. Special
capacitors, called electrolytic
capacitors, are made by depositing
a layer of insulating material on to
aluminium plates by electrolysis.
Different value capacitors hold
different amounts of charge
when the same voltage is passed
across their plates.

Modern components

Since the 1950s, many electronic components have been
made much smaller, and new ones have been developed.
They are now so small that miniature equipment is
becoming more and more common. Tiny components
called transistors, resistors, diodes, and capacitors are found
in many common electronic gadgets. New technology has
also produced more reliable components. For example,
light-emitting diodes (LEDs) are often used instead of
indicator bulbs because they hardly ever go wrong.

Light-

dependent

resistor

On the front of this night-light is a
resistor that is sensitive to light. Its
resistance increases when it gets
dark. Electronic circuits detect this
change and let the current through
to switch the light on at night.

RESISTORS

The amount of current flowing in
a circuit can be controlled by
resistors: a resistor with a high
resistance will only let a relatively
small current flow. Variable
resistors, made from carbon or
wire, have a sliding contact so
that the resistance can be varied.
Light-dependent resistors (LDRs)
decrease in resistance with more
light. Most thermistors decrease
in resistance when their
temperature rises.

CAPACITORS

AMPLIFIER

An amplifier contains a circuit
that makes a small electric signal
bigger. Transistors feed the
amplified (stronger) signal to
the loudspeaker.

Emitter

Base

Collector

WHAT’S IN A TRANSISTOR
This transistor is made of a layer
of p-type semiconductor
sandwiched between two layers of
n-type semiconductor. The middle
layer is the base of the transistor
and the outer layers are the
emitter and the collector.

TRANSISTORS

Transistors are components that
amplify electric current. They can
also switch current on and off.
Transistors vary in the frequency
range of signals they can handle.
Most transistors consume just a few
milliamps from a supply of 12 volts
or less. Transistors handling high
power become hot and may have
finned metal devices called heat
sinks to help radiate the heat.

HOW A TRANSISTOR WORKS
A small change in the current
flowing into the base causes a larger
change in the current flowing
through the collector. So when a
small signal is applied to the base, a
larger signal appears at the
collector. Strengthening a signal in
this way is called amplification.

DIODES

Diodes will only let the current in
an electronic circuit pass in one
direction. This means they can
change alternating current into
pulses of direct current. Some
diodes are designed to cope with
weak currents; others can handle
very high currents. Other diodes,
called light-emitting diodes
(LEDs), give off light.

Light given out
as current
passes through

Semiconductor

junction

WHAT’S IN
AN LED
Light-emitting
diodes are made

of a semiconductor

junction encapsulated in plastic.

It gives out light when a current
passes through. LEDs hardly ever
fail, and are used instead of bulbs.

LIGHT-EMITTING DIODES
Light-emitting diodes (LEDs)
are used in some calculators for
the numbers or as indicators on
electronic panels. Columns of
LEDs form the sound level
indicators on some amplifiers.

As the sound levels increase,
more LEDs in a column light up.

Find out more

Electrolysis p.67
Current electricity p. 148
Circuits p.152
Radio p.164

Integrated circuits p.170
Calculators p.172
Fa ct finder p . 410

169

ELECTRICITY AND MAGNETISM

Integrated circuits

inside a chip

This is part of the surface of a
silicon chip (integrated circuit),
magnified 40 times. Connections
to other circuits are made through
fine wires welded to pads around
the edge of the chip.

INSIDE AN ELECTRONIC GAME, one tiny part controls everything that
the game can do: move characters around the screen, keep a record of
the score, bleep when you win or lose. The tiny part is an integrated
circuit (also called a silicon chip), which is a complete circuit in
miniature; it is a few millimetres square. All the necessary electronic
components are on the chip, and there are thousands of them on
the one tiny slice of silicon. Integrated (all-in-one) circuits

perform the same kinds of tasks as circuits made from separate
electronic components. Chips are cheap to make, and are
very reliable, so they have made electronic equipment
cheaper, more efficient, and smaller.

CIRCUITS IN MINIATURE
Many integrated circuits
are formed at the same
time on a silicon wafer,
which is a slice from a
crystal of pure silicon. After
manufacture, each
individual circuit is tested
electronically. Those that
pass all the tests are
mounted in protective
plastic or ceramic capsules.

N-type

semiconductor for
outer electrodes

Hand-held electronic games
are dedicated electronic
computers, which means that
they are programmed and used
to do one thing only. This game
displays a space scene on the
screen and allows players to fire
at the enemy spacecraft.

DESIGNING A CIRCUIT
Before an integrated circuit can be
made, a large plan of the whole
circuit is drawn and checked for
accuracy. As integrated circuits are
built up in layers, a plan for each
layer is then designed and drawn
up. A chip-sized version, called a
mask, is made from these plans.

CIRCUIT BOARD
Some simple devices have one
main chip and few other
components. But more
complex equipment, like
a computer, may have
many chips mounted on a
printed circuit board, which
has the connections between
chips and other components
“printed” on in copper.

Chip in the centre of
a ceramic capsule

Silicon dioxide

P-type silicon

The connections to
electrodes are made of
a conductor, aluminium.

Silicon dioxide

This is a transistor, just one-
thousandth of a millimetre wide.

These connect
the chip to the
circuit board.

CHIP IN A CAPSULE
A “chip” seen on a circuit board
is actually a capsule that protects
a chip inside. Connections from
the chip to the circuit board
are made with fine gold wires
connected to the metal pins
that stick out of the capsule.
These are soldered to the
circuit board or plugged
into sockets.

Silicon dioxide
layer for
insulation

The silicon wafer is a
p-type semiconductor.

MAKING CHIPS
The components in a
chip are made by laying
p-type and n-type
semiconductors and other
materials on the silicon base,
using masks as guides. Heat
and chemicals are used to shape
the materials. The different
combinations produce dif ferent
components, such as transistors,
diodes, resistors, and low-value
capacitors. These are three of the
many stages involved in producing just
one component on the chip, in this
case a special type of transistor with an
insulated central electrode.

Polysilicon

transistor

electrode

170

ELECTRICITY AND MAGNETISM

Find out more

(

Soi

Electronic

COMPONENTS P.168

Calculators p.17<

JND RECORDING PC

Factfinder p.410

)

188

Logic gates

Logic gates work with
digital signals - usually the
presence or absence of a
small positive voltage. Truth
tables show what happens
when logic signals are
applied to logic gates. In a
truth table, the presence of
a signal is written as 1, and
no signal is written as 0.

Analogue to digital

Specially designed integrated
circuits are used to convert
analogue signals, like a sound
signal, to a digital form to be
stored on a CD, for example.
This gives a much better quality
of sound because it doesn’t get
distorted when you amplify it,
and it doesn’t pick up noises like
hiss from wear on a record. On
reception or replay, digital
signals are changed back into
analogue form. Analogue signals
are electrical copies of sound,
vision, or other signals, so they
vary continuously. Digital signals
consist of simple pulses that are
either on or off.

THE “AND” GATE
A two-input AND gate gives an
output when a signal is applied to
one input AND to the other input.

Output

i—r

Input
A B

Loudness-

255-i

Input A

Input B

Output

Electric signal created
by a sound wave

100 -

50-

THE “OR” GATE
A two-input OR gate gives an
output when a signal is applied to
one input OR to the other input
OR to both.

Output

Input

Input A

Input B

Output

o ^

The analogue signal is
measured and converted
into digital pulses at many

128

A digital signal is in binary
form, which means that it is a
sequence of on (1) and off (0).

The value of200 is converted into
the digital number 11001000, which
represents 128 + 64 + 8.

THE “NOT” GATE
A NOT gate gives an output when
a signal is NOT applied to its
input. It gives no output signal
when an input signal is present. A
Output I NOT gate is sometimes
called an inverter.

Input

Output

Input

MEASURING THE SIGNAL
To change an analogue signal into
a digital one, an integrated circuit
measures the strength of the
analogue signal thousands of times
each second. It then changes these
measurements into the right
pattern of digital signals.

As long as there is no ball in the red
slot (C), there is no input to the
NOT gate, so this normally gives an
output signal to the AND gate.

Using integrated circuits

This pinball game uses a simple integrated circuit
that contains several logic gates - each consisting
of a few transistors and other components. A logic
gate responds to the presence or absence of
incoming signals and gives the appropriate
output. The chip operates coloured light-
emitting diodes (LEDs) to show which slots
the balls enter, and to indicate win or
lose. To win, you must get at least one
ball in a blue slot and at least one in a
yellow slot, but none in the red slot.
The green light comes on if you
win. A red light means you lose.

A ball in either yellow slot sends a
signal to the right-hand OH gate. This
gives an output if there is an input
signal at “B” OH “D” (OH both). The
output lights the yellow LED, and
goes to the AND gate.

PINBALL CIRCUIT
When a ball rolls down a slot, it
connects the two metal contacts.
One of each pair of contacts is
connected to a small positive
voltage. So when a ball goes into a
slot, it causes this signal to be
applied to one of the gates. The
circuit is arranged so that an LED
of the right colour lights up when a
ball is in a slot. The power supplies
to the logic gates are not shown.

A ball in either blue slot sends a signal
to the left-hand OH gate. This gives an
output if there is an input signal at “A ”
OH “E” (OH both). This output lights the
blue LED, and goes to the AND gate.

Light-emitting

diode

The three-input AND gate gives an
output signal only when there is a
signal at all three inputs. So the AND
gate gives an output when you have a
ball in one OH other of the blue slots,
and in one OH other of the yellow
slots, and NOT in the red slot. The
output from the AND gate lights the
green LED to show that you have won.

Positive
' voltage

The output from (==
the red slot lights the
red LED. You lose if
this lights up.

OH gate

171

ELECTRICITY AND MAGNETISM

Calculators

KEYPAD

Switches behind the keypad close
briefly when you press the keys for
numbers and instructions (such as
+, -S-, or =). Electronic circuits

detect what you key in and store it
in binary form. Then other circuits
carry out the calculations.

Printed circuit board

A MODERN ELECTRONIC CALCULATOR is
a miracle of miniaturization, and it has more
computing power than a room full of early
electronic computing equipment. An electronic
calculator is a computer that does calculations
only. These calculations are done so quickly that
the result appears almost as soon as you press
the last key. Calculators have the basic functions
of add, subtract, multiply, and divide; they can
also have function keys that carry out complex
calculations automatically. Some calculators can
be programmed by the user to carry out
specific calculations.

DIFFERENCE ENGINE
This early calculator was the first one
designed by Charles Babbage. It had
more than 2000 moving parts.

Green insulating coating
protects copper tracks which
connect circuit components.

CPU (with
memory)

CALCULATOR CHIP
Modern pocket
calculators have just
one chip containing all the
complex circuits needed to
carry out the calculations. Inside
the chip, a central processing unit
(CPU) controls operations and uses an
electronic memory to store numbers used in
calculations and the results that are displayed.

Switch contacts
connect when
buttons on keypad
are pressed.

Input

(keypad)

BINARY SYSTEM

The decimal number 25, for example, is
11001 in binary. This represents 1x16, plus 1
x 8, plus 0x4, plus 0x2, plus lxl. This may
seem complicated to us, but it is very easy for
a calculator to represent, store, and recognize
each 0 or 1 as the absence or presence of an
electrical voltage. The binary number
calculated is automatically converted into the
decimal number shown on the display.

Integrated circuit

CHARLES BABBAGE

In the early 1830s, an
English mathematician
called Charles Babbage
(1792-1871) designed a
mechanical calculator
called the Analytical
Engine. It would have a
store, or memory, to hold
numbers. An arithmetic unit
would do calculations according
to instructions from a control
unit. Instructions (programs)
were to be fed into the machine
in code, as patterns of holes on
punched cards. In other words it
would have been programmable
(unlike his Difference Engines);
modern computers still operate
on these basic ideas. Babbage
devoted many years and
much of his fortune to
this machine, but it was
never completed.

Numeral

Output

(numeral

display)

Ribbon connector
connects the keypad to the
circuit board.

Number computer

Some people use their fingers to help
when counting and doing calculations.

This is why our system of counting and
numbering is based on tens. This decimal
counting system uses the ten digits 0 to 9.

Modern electronic calculators use
the binary system, with two digits,

0 and 1, instead. This is because
circuits designed to recognize
just two signal levels,

representing 0 and 1, are
simpler and more
reliable than

circuits designed
to recognize
ten signal
levels.

Resistor

Transistor

POCKET CALCULATOR
This pocket calculator has an extra
memory to store numbers needed
later while other calculations are
carried out. The calculator can also
work out square roots of numbers.

Mains power socket

Find out more

HOW SCIENTISTS WORK P.14

Cells and batteries p.150
Electronic

COMPONENTS P.168

Integrated circuits p.170
Computers p.173
Fa ct finder p . 410

O0008
00088
ooe=:
oiooDB

172

ELECTRICITY AND MAGNETISM

Computers

COMPUTERS CAN HELP YOU write letters, draw pictures, play games,
do calculations very quickly, and carry out many other tasks. For example, it
would take hours to calculate and write down the 12 times table up to
3,000 times 12. But a computer can do this and produce a neatly printed
and error-free table in minutes. Computers handle text by storing codes
representing letters of the alphabet, spaces, and punctuation marks. Using
a computer to write and edit text is called word processing. Computers also
allow you to produce graphics (lines and pictures) without ever touching
a pencil or paper. And in desk-top publishing, words and pictures are
combined using a computer to produce newspapers, books, and
magazines. With a suitable program (set of instructions) and hardware
(computer equipment), you can do all these things and more besides.

Home computer

A typical home computer system has
input devices to put programs and
data (information) into the computer.
Electronic circuits inside the computer
carry out the work and send the
results to output devices. Programs on
magnetic tapes or disks are fed into
the computer by playing them on a
suitable unit. Many home computers
now include special multimedia
facilities including built-in
microphones and speakers.

A keyboard is used for
entering data and commands.

The screen shows what the
computer is doing.
Messages on the screen
can tell you what to do next
or warn you of problems.

When the mouse is
moved, a ball
underneath rotates.
This movement,
changed into
electronic signals,
makes a marker move
over the screen.

INPUT DEVICES

When a stylus is
drawn over a graphics
tablet, the movements
are changed into
electric signals.

These make the
computer draw
matching lines
on the screen.

General-purpose computers have a
keyboard. This has all the letters
and numbers of a typewriter, plus a
few extra keys. The keyboard is
used to feed words and numbers
into the computer. It is also used to
type in commands, and to move
objects around the screen when
playing games. But other input
devices are sometimes more
useful. A joystick is better for
controlling moving objects
when playing games. A mouse
may be moved around the desk to
make a marker move on the screen.
A mouse can also be used to draw a
picture, but a graphics tablet is
easier to use for this. Musical notes
may be fed in from the “typewriter”
keyboard, but it is easier to use a
specially designed music keyboard.

To play some
computer games,
you use joysticks
to steer vehicles
around the screen.

STORAGE

The large amounts of information and
instructions that computers handle have
to be stored. The instructions that make
up programs are usually stored as pulses
on magnetic tapes or disks. These
instructions are fed into the computer and
stored there temporarily in memory chips.
Other chips in the computer are used to
store information permanently. Work
done on the computer is often stored on
magnetic tapes or disks.

One CD ROM (compact
disc read-only
memory) can
store a lot of
information, such
as the contents of
several books. .

Chips store
programs and
information as
electronic
signals.

Floppy disks are
used to save and
transfer information.

MINIATURE COMPUTER
A laptop or notebook computer
enables people to work while
travelling. Some store the work
in a memory that is continually
powered, while others have a
disk unit for storage.

The graphics /sound card changes
data into images that can be seen
on the screen and sounds that can
be heard.

Modem
means
modulator-
demodulator.

Modems
change
computer
signals so that
they can be sent
along telephone wires
between computers.

Many printers form letters and
pictures using combinations of dots.

OUTPUT DEVICES
You can usually see what
a computer is doing by
looking at its monitor
(screen). And you can
usually obtain a permanent
record, called a printout or
hard copy, by sending the
information in the computer
to a printer. Sometimes the
output of a computer is fed via
a telephone line to another
computer using a device called
a modem. Computers can also
interpret our instructions to
make robots move as we want.

173

Continued on next page

Continued from previous page

ELECTRICITY AND MAGNETISM

Hardware and software

To make a computer do useful
work, you need the equipment
(hardware) and a set of instructions j
(called a program or software).
Computers also need system
software, which tells them how to
operate. Computers work with
information and instructions in
the form of electronic signals
representing the Is and Os of the
binary code. Writing programs in
this form would take a long time.

So they are written instead in
special programming languages
that partly resemble English. These
are automatically changed into the
form that the computer understands.

MONITOR

The monitor, also called a VDU (visual display
unit), is often a separate unit with a cable to
connect it to the computer. Computer monitors
are designed to give a high-quality picture so
that words can be read from the screen without
causing eye-strain. Some computers have a
monitor permanently attached.

ECONOMY
MONITORING
Some cheap computers have a
modulator to make the signals
from the computer similar to
those that carry television
programmes. This allows the
signals to be tuned in and
displayed on an ordinary
television set. But the picture
quality is not as good as that of
a monitor designed for use
with computers, and words
may be hard to read.

COMPUTER

A personal computer is usually a box containing
the main electronic units and fitted with sockets
for connecting the mains supply, keyboard,
monitor, printer, and other equipment. Disk ■
units, called drives, are usually fitted inside
this box, but sockets are usually provided for
connecting other disk drives.

These red switches
are under the keys
on a keyboard.

Output on screen
or printer

KEYBOARD

The keyboard is simply

lots of push-button V^UNg||l

switches marked with

letters and other

characters. What happens IBB
when you press a particular VreEjJ
key depends on how the BEjp
computer is programmed.

For example, pressing the key may
make a letter of the alphabet appear
on the screen, or a character in an
adventure game may move around.

Input via
keyboard

Many computers have
a built-in hard (rigid)
magnetic disk ^
drive to store ?A
programs and Hl
data. Most hard
disks cannot be
removed from the ^
machine.

COMPUTERS

CPU

The central processing unit (CPU)
is the computer’s centre of
operations. It consists of large
numbers of electronic circuits, all
contained in a single chip called a
microprocessor. The CPU takes in
data from the keyboard, the ROM,
and the RAM. It can also send data
to be stored in the RAM, and send
data to the monitor (and other
output devices).

1642 Blaise Pascal (1623-62) builds
a mechanical calculating machine.

1805 Joseph Jacquard (1752-1834)
buildsan automatic loom. The
patterns are controlled by punched
cards. Cards are later used in
computers.

1833 Charles Babbage designs the
first general-purpose programmable
computer, the Analytical Engine.

1890 Herman Hollerith (1860-1929)
uses a punched-card system to make
the United States census calculations
hundreds of times faster.

1946 Engineers in the United States
build the first electronic digital
computer.

1951 The same team build the first
mass-produced computer, UNIVAC 1.
Micrographof an integrated circuit

Floppy disks, in protective
plastic cases, and hard disk
cartridges can be removed
from the computer. ^

Hard disk

MEMORIES
Chips called the ROM
(read-only memory) store
Y information permanently

needed by the computer. Other
chips make up the RAM (random-
access memory). The ROM is like a
book: the computer gets information
it, but does not add to it. The RAM is
like a notebook: the computer puts information in
it and can use the information and alter it. But
information in RAM is lost when the machine is switched
off. Disks are also storage devices. Floppy disks are useful
for transferring information between machines.

Find out more

Floppy disk Cartridge
Chip

HOW SCIENTISTS WORK P.14
Magnetism p. 154
Television p.166
Integrated circuits p.170
Calculators p.172
Using computers p.175
Factfinder p.410

174

ELECTRICITY AND MAGNETISM

USING COMPUTERS

Trainee pilots feel all the forces that give
them the feeling of flying a real aeroplane
because controls in the cockpit move huge
pistons that tilt the simulator.

THE INTERNET
The Internet is an international
network of computers, modems,
and telephone lines. Computers
connected through the Internet can
send messages to, access information
from, and run programs on other
computers in the network. Most traffic
on the Internet is electronic mail
(e-mail). This is a cheap and speedy
way to send messages across the world.

VIRTUAL REALITY
Virtual reality is a way of going
into a world completely created
by a computer. The computer
creates 3-D images and stereo
sound in a special helmet
connected to a hand-held unit.
Any move you make with the
hand unit is transmitted to the
headset, so that you appear to
be interacting with the events
happening on the screen.

ALAN TURING

The British mathematician Alan
Turing (1912-54) was a major
contributor to theories used in
modern computing. He helped to
develop the electronic device and
the ideas used to decode German
secret messages during World
War II (1939-45). He was the
first to suggest that computers
could be “intelligent”.

“REAL” WINDOWS
Computer graphics are used
to create realistic views in
the “windows” of a flight
simulator. These change
just like real views in a
real aeroplane would.
This is very important,
to give the trainee
pilots a proper sense of
what it feels like to fly
an aeroplane.

MOST HOME COMPUTERS have several programs so they can be used
in different ways, for games as well as word processing, for example. But
many computers are dedicated machines. They do just one thing and
look quite different. For example, a bank’s cash-dispensing machine
uses computer technology to check people’s accounts and allow
them to withdraw money. The machine at
the bank is a computer terminal that is
connected to the bank’s central
computer, where details of all
accounts are stored. Dedicated
computers are also used to
control industrial processes
and transport systems, and
simulate real-life situations
(like flying a plane) for
research and training.

CAD

Computer-aided design
(CAD) is a way of designing things using
computer graphics. Information is fed into the
computer, which “constructs” the object on the
screen. Different operating conditions are fed
in too, and the design is tested. This helps to
identify parts of the design that are not good
enough so they can then be improved.

When the
packets arrive
at the correct
address they
are reassembled
into a readable
message.

Simulation

Pilots can become experts at flying
complex modern aeroplanes before
ever getting into a real one. The
trainee pilots are trained on computer-
controlled machines called simulators.

The computer makes the simulator react
just like an aeroplane would: the simulator
moves around, and the controls even give
realistic readings of things like height and
how much fuel is left in each tank.

This car design is being tested
for wind resistance using a
CRAY supercomputer.

To be transmitted,
the e-mail message
is divided into tiny
packets of data.

Find out more

HOW SCIENTISTS WORK P.14

Computers p. 173
Robots p.176
Electronic sounds p.189

175

ELECTRICITY AND MAGNETISM

Robots

BOMB DISPOSAL
Bomb disposal
experts can check
safely for bombs, thanks
to this mobile robot.
Closed-circuit television
cameras on the robot send
back pictures to the
controller. He or she uses
the pictures to check
objects suspected of being
bombs. The robot also has
floodlights for getting
clear pictures at night.
The remote-controlled
grab on the end of the
\ arm is used to pick up
\ a suspicious object.

ROBOTS IN FICTION
The robots from the film
Star Wars are human like:
C3PO can communicate in
three million ways, and R2D2
can repair spaceships. Real
robots will never need to be
so versatile, but some can
already do simple translations
and others can do repairs.

Signal to
gripper

Contrc

circuit

Gripper

Signal from
sensor

Aerial for
communication
with controller

FEEDBACK

The grippers on a robot
arm could crush fragile
objects when picking
them up. So pressure
sensors are provided
to detect when the
grippers have a firm hold.
The sensors feed an
electric signal back to a
control circuit, which
then stops any further
pressure being applied.

Floodlight

Tracks for
moving over
rough ground

Case under
investigation

The Vikings were sent to Mars
in two parts. An orbiter carried
and protected the lander until
reaching orbit around Mars.

The Viking lander is the
most complex robot to
have been sent into space.

W MARS MISSION
’ Vikings landed on Mars in
1976! These Vikings were two
robot landing craft, sent by
American scientists to search
for life on Mars. The
machines scooped up soil
and tested it for the presence
of living organisms in a
specially built biological
laboratory. No life was found,
but there could be life
elsewhere on this red planet,
and it could be in a different
form - Viking looked only for
life based on organic
chemistry, as it is on Earth.

INDUSTRIAL ROBOTS
Robots like this weld together metal
parts to make cars. Other robots
spray the car bodies with paint.
Unlike humans, robots never get
fed up with doing the same work
every day. They can also work for
much longer without stopping.

Find out more

Carbon p.40
Computers p.173
Mars p. 289
ip ACE PROBES P.301

[

176

SOUND AND LIGHT

The SOUNDS AND SIGHTS of the world are carried to us
by energy in the form of sound and light. In some ways,
sound and light are very similar. The energy of both is Jk
carried from one place to another by waves. The JBk

energy of sunlight warms the Earth, tans fair skin,
and makes plants grow. The energy of the sonic
boom - the bang made by a jet breaking the sound M
barrier - can shake buildings and shatter windows, fl
In other ways, sound and light are different. Sound
can only travel through matter - through gases ■ tfr

such as the air, through liquids, and through solids. II
Light can travel through a vacuum. We see light
from the stars that has been travelling for ^SB
thousands of years before reaching our eyes.

SOUND PICTURES

Cameras collect light to create images on
film and on television screens. Sound can
produce images too. This image of a
foetus inside the womb was made with
sound echoes. The echoes are made when
very high-pitched sound waves -
ultrasonic waves - travel through the
mother’s body. These are recorded
and used to build up a computer d

image of the unborn baby.

A Thunder

Jm AND LIGHTNING

■F A lightning strike releases huge
" amounts of sound and light

energy. The crash and flash of the
storm can be heard and seen from a
great distance. We see the lightning
before we hear the thunder because
light travels nearly a million times
faster than sound. We see the flash
within millionths of a second of it
happening, but may not hear the
thunder until several seconds later.

Image is
artificially
coloured.

SILENT JAR

The Ancient Grtfek philosopher Aristotle believed that both
sound and light travelled through the air like waves in the
sea. He also believed that neither could travel through a
vacuum. But it was not until the 17th century that scientists (
were able to create a vacuum to test Aristotle’s theory. One /
experiment was by the Irish scientist Robert Boyle in 1658. fif
He slowly pumped air out of a glass jar containing a JBt
ticking watch. The sound of the ticking disappeared
completely as the jar was emptied. Boyle concluded
that sounds are carried by air to our ears.

Aristotle had been right about sound. .

Robert Boyle

The sound of the
ticking watch
became fainter as
air was pumped out
of the jar.

This spray of optical
fibres is made up of
2,000 individual
strands.

QUIET SPACE
There is no air in
so there are

■F COMMUNICATIONS

Both sound and light enable us to
r communicate. We use our voices to talk, and
need light to see each other. Telephone systems
convert the sounds of voices into electrical signals
WF that are transmitted by cable and satellite to every part
of the world. Modern communications networks use
optical fibres to carry information. Pulses of light carry
telephone calls, television pictures, and computer data along
cables made from fine glass fibres.

space, _

no sounds there.

Astronauts talk to each J

other using radios because, m

unlike sound waves, radio
waves can travel through space.
Astronauts are able to see each other
because light, like radio waves, can travel
through a vacuum.

177

SOUND AND LIGHT

WE LIVE IN A WORLD full of sounds. Some occur naturally:
thunder, ocean waves breaking on the shore, the wind in the trees.
Others are made for a purpose: birds sing to attract a mate, bats
squeak to locate their prey, people speak to communicate. Some
sounds are just noise - annoying sounds that pollute the
environment: the roar of traffic, aircraft, and factory
machines. All sounds are caused by vibrations - the
rapid motion of particles of matter colliding with
each other and passing on energy as a
travelling pulse or wave. You can feel sound
vibrations. Place your fingertips against
your throat when you speak, or gently
touch a bicycle bell as it rings.

Direction of wave

VIBRATIONS

A gong vibrates when it is struck - it
flexes backwards and forwards rapidly.

The vibrating gong pushes to and fro on
the air molecules around it, making the air
pressure rise and fall. These pressure changes
are passed on by collisions between air ,
molecules and a sound wave travels away from
the gong. The parts of the wave where the air
pressure is increased (air molecules are
bunched up) are called compressions. The parts
where the pressure is decreased (air molecules
are spaced out) are called rarefactions.

impression

Pull end of spring in/
and out to send a
longitudinal wave along
the spring.

Move end of
spring up and
down to send a
transverse wave
along the spring.

WATERY SOUNDS

Sound travels faster in
water and loses its energy
less rapidly than in air, so
underwater sounds travel
further before dying away.
Whales and dolphins use
underwater sounds to
communicate and to
navigate. Some whales
“sing” songs that carry for
hundreds of kilometres
through the oceans.

Transverse and longitudinal

When you throw a stone into water, waves spread out
from the splash and move across the water. The surface
seems to vibrate up and down at right angles to the wave
direction. This kind of wave is called a longitudinal wave.
You can send both longitudinal and transverse waves
along a coiled spring.

SEISMIC WAVES
Earthquakes and explosions
generate seismic waves - sound
waves that travel through the
ground. The vibrations made by
these waves are recorded on a
seismograph. By studying these
waves, seismologists can sometimes
predict earthquakes, and can also
learn about the interior of the Earth.

WAVES OF ENERGY
A travelling wave carries energy
from one place to another. For
example a water wave passing a
buoy makes it bob up and
down energetically. But the
vibrating particles do not
themselves travel along the
wave. They just move to and fro
about the same spot - like the buoy
on the water’s surface.

Vibrations produced by the quake or
explosion are recorded on the
seismometer screen.

Motion of wave
lifts buoy up.

Buoy falls as the wave of
energy passes on.

178

SOUND AND LIGHT

lil

Speed of sound

In 1708, William Derham (1657-1735) became
one of the first people to establish the speed of
sound accurately. He stood on top of Upminster
Church in Essex, England and watched as a
cannon was fired 19 kilometres (12 miles) away.
He timed the interval between the cannon
flash and the boom, taking an average of
several measurements to allow for changes
in wind direction. His result was close to the
modern value of 343 metres (1130 ft) per
second at a temperature of 20°C (68°F).

The speed of sound in air
changes with the temperature.
At CPC (32°F), it is 331 m
(1086 ft) per second. At 40°C
(104°F), it is 354 m (1161 ft)
per second.

Sound

travels at
~ 343 m

(1130 ft) per
second through air
at20°C (68 °F).

Sound travels through
water at 1500 m A
(5000 ft) per M
second.. A H

TAPPING MESSAGES
Workers building the Channel
Tunnel linking the United Kingdom
to Europe sent messages by tapping
on pipes. Sound travels farther and
faster in metal than in air.

DIFFERENT SPEEDS
Sound travels more quickly through solids
and liquids than through gases. Solids and
liquids are “stiffer” than gases because the
molecules are closer together. They spring
back into shape more readily when they are
compressed, passing on sound pulses more
quickly. Sound travels nearly five times
faster in water than in air, and almost
20 times faster in steel.

SHOCK WAVES
Supersonic jets fly faster than the speed of
sound, so you cannot hear them coming
towards you - the jet passes you before the
sound arrives. But when

_ the sound catches up, it

arrives suddenly
J as a shock wave that

produces a sonic boom.

Sound waves spread
ahead of a jet flying at
less than the speed of
sound so you hear it
approaching.

Sound travels
at 6000m
(20,000 ft) per
second through steel.

Sound waves pile up in
front of a jet travelling at
the speed of sound. They
form a large shock wave.

Shock wave

ERNST MACH

I More than fifty years before the first
supersonic flights, Austrian
physicist Ernst Mach (1838-1916)
described how shock waves are
formed. Today, Mach numbers
Ofc are used to give aircraft speeds in
terms of the speed of sound. An
aircraft flying at the speed of
mL sound is flying at Mach 1. Mach 2 is
twice the speed of sound. All
wp passenger aircraft, except Concorde,
are subsonic; they fly below Mach 1.
Concorde is supersonic; it flies at Mach 2.

When the jet
breaks the sound
barrier, it leaves a shock
wave behind it. This shock
wave produces a sonic boom
as it passes over the ground.

WHIP CRACK

The loud crack a whip makes may
well be because the tip of the whip
moves faster than the speed of
sound; generating a shock wave.

Find out more

St.

Prop

ATES OF MATTER P.

'ERTIES OF MATTER

Bonding p.28
Vibrations p.126
ARTHQUAKES P.22C

p.22

)

179

SOUND AND LIGHT

Measuring sound

The microphone, which is
connected to the
oscilloscope, converts the
flute’s sound into
an electrical ; . Aw
signal.

Sounds CAN BE LOUD OR QUIET, high-pitched like a
, whistle or low-pitched like a car engine. Some sounds are
pleasant, others are annoying or even painful. But what makes
one sound different from another? It is nothing to do with
speed. All sounds travel at the same speed. If sounds did travel at
different speeds, the sounds of instruments in an orchestra
would reach your ears at different times and the music would be
jumbled. The answer is that different sounds have differently
shaped waves. The feature of a sound wave that makes it quiet or
loud is called its amplitude. The feature that makes the sound
high-pitched or low-pitched is called the frequency. The
wavelength - the distance between two wave compressions

(crests) - also affects the sound.

i ' - High amplitude

- a loud

HEINRICH HERTZ

The German physicist
Heinrich Hertz (1857-94)
was the first to produce
and detect radio waves.
The unit of frequency
used for all kinds of waves
and vibrations - including
sound waves, radio waves,
and light waves - is named
after him. One Hertz
(1 Hz) is equal to one
vibration per second.

Amplitude j

An oscilloscope displays the pattern
of a sound wave on a screen. The
pattern traced on the screen shows I
how the air pressure rises and falls as
the sound wave passes the micro¬
phone. If the sound is made louder,
the pressure changes are greater and
the amplitude of the wave is increased,

Low
amplitude -
a quiet sound

As the car drives past,
sound waves become
longer, and sound lower.

Siren of approaching car
produces short, high-
frequency waves.

High-frequency
wave - a high-
pitched

sound . Nc-

FREQUENCY
The frequency of a wave is the
number of vibrations it makes in one
second. This is measured by counting
the number of wave crests that pass
in that time. A wave with a low
V frequency has a long wavelength.
A wave with a high frequency has
a short wavelength. High-
frequency, short wavelengths
7 make high-pitched sounds. Low-
frequency, long wavelengths make
low-pitched sounds.

Low-frequency
wave - a low-
pitched sound

Peaks of a ~—

high-frequency sound wave on the
screen are closer together than lower '
frequency wave peaks because they
arrive at the microphone more frequently.

THE DOPPLER EFFECT

The pitch of sound you hear as a police car speeds
by depends on whether the car is moving towards
or away from you. As the car approaches, the sound
waves ahead of it are bunched up. These short
waves have a high frequency, so the siren sounds
high. Behind the car, the waves are stretched out.
These longer waves have a lower frequency, so the
siren sounds lower as the car drives past.

SOUND WAVES

Sound waves actually travel through
air like a wave along a coiled spring.
A compression (where the air
molecules are bunched up)
corresponds to the crest of a water
wave. A rarefaction (where the air is
more spaced out), corresponds to
the trough of a water wave.

Compression

Rarefaction

Trough

WAVELENGTH
Short and long waves are easy to
see in water. The wavelength of a
water wave is the distance
between two neighbouring crests.

Long wavelengths

Find out more

Short wavelengths

The wavelength of a sound wave
is the distance between two
neighbouring compressions. In a
short wavelength sound, the
waves are close together. If the
waves are farther apart, the
wavelength is longer.

Sound p. 178

Making and hearing sounds

p.182

Loudness p. 181
Musical sounds p.186
Factfinder p.412

180

SOUND AND LIGHT

Loudness

Ear protectors

People
should
spend only short
periods working in sound
levels over 100 dB.

The LOUDNESS OF A SOUND depends on the intensity
(amount of energy) the sound waves carry. Big vibrations have
a lot of energy and produce intense sound waves with a large
amplitude. Very loud sounds, such as sonic booms and shock
waves from explosions, can be painful and sometimes cause a
lot of damage - the sound waves bang into structures and
cause them to vibrate. A special scale called the decibel scale,
named after Alexander Graham Bell, is used to measure the
loudness of sound.

The decibel scale

The difference in amplitude between
the quietest sounds and sounds so
loud they hurt is almost too great to
write down in numbers. The decibel
scale is an example of a logarithmic
scale. Every time another 10
decibels (dB) are added to the
sound level, the loudness of the
HIDDEN DANGER sound is multiplied by 10. Increasing

A personal stereo does not the amount of sound by 20 dB

produce much power, but because multiplies the loudness by

nearly all the sound goes directly 10 X 10= 100 times,

into the ears, the sound levels
inside the ear can be very high.

Playing personal stereos too loud
for too long can cause hearing loss.

120 dB

100 dB

80 dB

• rJi.

The sound
of a rock
group is like
the sound of
100 million
falling leaves!

It is not
uncommon for
rock musicians to suffer hearing
losses. Sounds over 120 dB can
cause intense pain and deafness.

EAR PROTECTION
People who have to work
surrounded by loud sounds must
protect their ears. They wear ear
protectors to muffle the noise.
Prolonged exposure to high
sound levels causes hearing loss at
certain frequencies.

MEASURING SOUND
Sound levels inside factories can be
monitored with sound level meters
to make sure the levels are not
dangerous. The level should not
exceed 110 dB at any time. For a
full working day, the level
should not exceed 90 dB.

ANTI-NOISE

It is possible for two sounds to add together
to make silence! This is unlikely to happen
by chance, but if a sound wave is measured,
a computer can produce its mirror image.

The peaks of the original sound wave
correspond exactly to the troughs in the
new sound wave. When the two sounds
overlap, they cancel each other out. This
method is called “anti-noise”. In hospitals, some
body scanners are fitted with anti-noise systems
to make them quieter for the patient. Future
refrigerators and washing machines fitted with
anti-noise systems may be completely silent. Trough _

Peak

Sound is
cancelled

jOUt.

Find out more

Tele<

Vibrations p.126

COMMUNICATIONS

Sound p.178

LJSICAL SOUNDS P.l

p.162

181

SOUND AND LIGHT

Making and hearing sound

If YOU HAVE EVER LOST YOUR VOICE, you know how difficult it is to
make people understand you without it. Speech is our main form of
communication. When we speak, we produce vibrations that travel
through the air as sound waves. These sound waves are changed into
sounds we can recognize with our ears. Although our ears can detect
sounds in the range of 20-20,000 Hz, they are most sensitive to sounds
with frequencies of around 1,000 Hz. This is the frequency range of
voices in normal conversation, although our voices may contain sounds
as low-pitched as 50 Hz and as high-pitched as 10,000 Hz. Just as we use
our voices to talk to other people, animals use the sounds they make to

communicate with each other.

Making sound

We produce our voices by forcing air
from our lungs past the vocal cords in
our throats. The rushing air makes the
cords vibrate. When we speak and sing,
we make constant adjustments to the
tension of our vocal cords, the shape of
our mouths, and the speed of the
projected air. In this way, we control the
pitch, quality, and loudness of our voices.

RESONANCE

Most objects can vibrate. The frequency at
which an object vibrates naturally is called its
resonant frequency. If a sound of exactly that
frequency is played near the object, it picks up
energy from the sound wave and vibrates in
sympathy. This is resonance. You can often hear
resonances when you play loud music in a room.
A particular note will cause a door panel or an
object near the speakers to resonate. If a singer
sings with a frequency equal to the natural
frequency of a wine glass, the glass may resonate
so strongly that it shatters.

If a sound comes from the right,
sound waves reach the right ear a
split second before they reach the left
ear. This is why you can tell which
direction the sound is coming from.

Hearing sound

Sound waves collected by the outer ear
force the eardrum to vibrate. These
vibrations are carried on to the inner ear
through a series of tiny bones. Fluid inside a
narrow tube, the cochlea, vibrates. These
vibrations stimulate tiny hairs on nerves.
These nerves send electrical impulses to the
brain, which enables us to
recognize the sound.

The aid can b e adjusted
to amplify particular
sound frequencies.

AIR IN BOTTLES
You can see and hear how
dif ferent amounts of air
vibrate to give different
sounds by blowing across
the top of bottles. If you
blow across the top of an
empty bottle, the air inside
vibrates at its resonant
frequency. Pouring water
into the bottle changes the
volume of the air and
alters the pitch of the
note. Short columns
j of air vibrate more
quickly and give a
higher pitch than
long air columns.

Volume control

DEAFNESS
People who have some hearing
loss, but who are not completely
deaf, can be helped by wearing a
hearing aid. This consists of a
miniature microphone, amplifier,
and loudspeaker. Sounds arriving
at the microphone are amplified
and fed into the earpiece.

_ Earhook

182

SOUND AND LIGHT

ANIMAL SOUNDS

Animals are able to make a wide range of sounds.
Despite their relatively small size, some frogs can
produce very low-pitched croaks. They do this by
puffing up an air sac under their throats until it is
nearly as big as they are. Howler monkeys
produce some of the loudest sounds in the
animal kingdom. They have special spaces in the
bones behind their nostrils that they force to
resonate with powerful blasts of air. Insects do
not have lungs, so they cannot blow air to make
sounds. But grasshoppers can make a chirping
sound by brushing stiff hairs
on their leg*

Cone is made
from paper or
plastic.

Wire coil moves in
step with electrical
signals.

LOUDSPEAKER
Sound is recorded and replayed by
converting it to an electrical signal.
Before we can listen to a record, tape,
or compact disc (CD), these signals
have to be converted back into sound
by a loudspeaker. The electrical
signals are fed to a wire coil
surrounded by a magnetic field inside
the loudspeaker. The changing signals
cause the cone on the outside of the
speaker to vibrate, generating sound.

The screams of a
howler monkey can be
heard for distances up
to 16 km
1(10 miles).

Magnet
produces
magnetic field.

Moving-coil loudspeaker

Bats can make and hear
ultrasound frequencies. The high,
squeaking sounds they make
bounce off objects, helping them to
locate prey such as flying insects.

Howler
monkey
400-6000 Hz

Grasshopper
7000-100,000 Hz

Human
85-1100 Hz

Dogs are able to hear the
high-frequency sounds
made by special whistles
that sound silent
to us. . -to

Diaphragm is
made of plastic
or thin metal foil.

Magnet

Wire coil is fixed
to diaphragm. ^

PyF MICROPHONE

Before sounds can be
recorded, they need to
be converted into electrical
signals. A moving-coil
microphone uses the same system
as a moving-coil loudspeaker, but in
reverse. It contains a wire coil fixed to a
flexible disc. Sound waves make the
diaphragm and coil vibrate. The
movement of the coil within a magnetic
field generates an electric current in the
coil. The current fluctuates in the same
way as the sound wave.

Bat ^
1000 -
120,000 Hz

Dog

15-50,000 Hz

HEARING RANGES
Most animals can hear more
frequencies than they can produce,
and can make sounds well outside
the range of our hearing. The
range of frequencies we can hear
changes as we get older. A child
can detect frequencies from 20 -
20,000 Hz. But a typical 60-year-
old can only hear sounds with
frequencies up to about 12,000 Hz.

VOICE ACTIVATION

A simple sound-activated toy, such as this dancing flower,
has a microphone that triggers movement when it
detects sounds above a certain level. A more
sophisticated voice-activated system can give
information about a customer’s bank account when it is
called by telephone. Recognizing words spoken by
different people is very difficult, but computers that can
respond to individual voice patterns are now being
developed for everyday use.

Find out more

Vibrations p.126
Electromagnetism p.156
Electronic components p.168
Measuring sound p.180
Reflection and
absorption P.184
Senses p.358

183

SOUND AND LIGHT

Reflection and absorption

ECHOES

If you stand some distance away

Have you ever wondered why your voice sounds

fuller and more powerful than usual when you sing in the bath?
It is because sound waves are reflected by smooth, hard surfaces
such as the bathroom walls. They bounce off like a rubber ball
bounces off the walls in a squash court. Although the direction
of the sound waves changes, their pitch is not altered. As well as
being fun, echoes '(sound reflections) can be useful. Before the
days of radar, sailors caught in fog could tell how far they were
from dangerous cliffs by sounding the ship’s fog horn and
timing the interval before the reflection was heard. But sounds
are not always reflected. If they meet a soft surface, such as a
cushion, they will be absorbed and will not bounce back.

Carefully positioned panels
reflect sounds from the
stage towards the
audience.

Acoustics

The way sound echoes around a
building is called acoustics. Large
buildings can seem full of echoes,
especially if they have many bare
surfaces. Reverberation occurs
when sounds echo around for
several seconds. In a concert hall
it is important to control the
echoes. If there is not enough
reverberation, the music
sounds thin with no
sparkle. Too much
reverberation, and
the sounds are jumbled.
Special panels direct
sound reflections
towards the audience.

Others, along with
curtains, absorb excess
reverberation.

Reflecting

panels

fronva wall and make a sound, it
will be reflected back to you
shortly after. The time it takes
depends on how far away the wall
is. If you are standing 50 metres
(164 ft) away, the sound has to
travel there and back - a distance
of 100 metres (328 ft). Dividing
100 metres by the time taken
between making the sound and
hearing the echo will give you the
speed at which the sound is
travelling.

Sound-absorbing
panels

ANECHOIC CHAMBER
The sound-absorbing panels in the walls
and ceiling of an anechoic wind tunnel
reduce reverberation. This enables
scientists to measure accurately the noise
generated by an aircraft propellor.

Curtains
and the bodies
of people in the
audience absorb
sound, reducing
reverberation.

SOUND DISHES

Parabolic dishes are used to
collect and concentrate
sound. Their special
shape reflects and
concentrates any
sound coming from
directly in front of the
dish towards the microphone
at the centre. In this way, the
microphone receives more sound
energy than it would without the
dish. Parabolic dishes make it
possible to record low-level
sounds such as bird song.

SOUND ABSORPTION
Soft surfaces absorb sound energy in
the same way as sand absorbs energy
from a ball thrown onto it In this
room, the rug, curtains, sofa, and
plant all absorb sound energy so
that it does not bounce back.

SOUND REFLECTION
Smooth, hard surfaces reflect
sound energy in the same way as a
ball bounces off concrete. In this
room, the sound from the stereo
speakers bounces off the floor,
walls, and wooden chair.

184

SOUND AND LTGHT

Limbs

Abdominal

wall

Echo

signals

HOW ULTRASOUND WORKS
Ultrasound works by recording
echoes as a series of spots.
The brightness of each one
varies according to the
strength of echo received.
This image of a foetus was
built up by computer from a
compilation of scans.

Ultrasonic image
synthesized from
scans

ECHOLO CATION

Dolphins use ultrasound frequencies to

ECHO-SOUNDING reflects the sound

As a result of the Titanic disaster in back.

1912, when the ship collided with an

iceberg on her maiden voyage, French scientist

Paul Langevin led research projects to develop

sonar. Sonar uses reflected ultrasound waves to

locate icebergs, shoals of fish, wrecks,

submarines, and to measure the depth of water

under a ship. Pulses of sound are transmitted

into the ocean. Any echoes bouncing back from

an object are monitored. The time delay

between transmitting a pulse and receiving its

echo indicates how far away the object is.

SCREEN IMAGE
This image of a shipwreck was
produced by scanning the direction
of the outgoing sound. The patterns
of echoes were then gradually built
up on a computer screen.

Metal component is
immersed in water,
which acts as a
conducting medium for
the sound.

Ultrasound

Sound waves with frequencies above 20,000 Hz are
beyond the range of human hearing. Sound with a
frequency greater than this is described as ultrasound,
or ultrasonic. Ultrasound is often used in medicine
because, unlike X-rays, ultrasonic waves do not damage
human tissue. A scanner transmits ultrasound waves
into the body, where they are reflected by different
organs. The scanner receives these reflections back
and displays them as an image on a screen.

Clicking sounds are
produced by a special
organ on the
dolphin’s head.

The ship’s sonar
under the keel
transmits high-
frequency sound
waves into the
water.

The time it takes the
reflected sound wave to
come back indicates the
shipwreck’s depth.

NON-DESTRUCTIVE TESTING
Important components in aircraft must
not contain hidden flaws. Tiny internal
cracks could grow and cause a
component to fail when an aircraft is in
flight. Non-destructive testing (NDT)
uses ultrasound as a means of spotting
such flaws without damaging the
component. Pulses of ultrasound are
reflected by any cracks, which show up
in ultrasonic images
on a screen.

communicate with each other and also to locate fish
and underwater obstacles. The loud clicking sounds
the dolphins produce bounce off objects and make
echoes. These echoes enable dolphins to tell the size
and distance of objects in the water
around them. This
system is invaluable
when it comes to
detecting predators
such as sharks.

Find out more

Soi

Make

JND AND LIGHT P.

ASURING SOUND P.

NG AND HEARING S<
p.182

Mammals p.334

177

180

OUND

185

SOUND AND LIGHT

Musical sounds

Long, thick strings make
low-pitched notes. Short,
thin strings make high-
pitched notes. - _

Soundboard resonates
and amplifies the
sound of the piano.

All MUSICAL INSTRUMENTS work by making air
vibrate. Players control the frequency and amplitude of
the vibrations to play tunes and make rhythms. The
distinctive timbre (quality of sound) of an instrument
depends on the way the air vibrates. Musicians blow air
into wind instruments either across a hole or past a
flexible reed. The air inside a flute, which does not
have a reed, vibrates simply to make a pure, sweet
sound. Air blown past the reeds inside bagpipe tubes
vibrates in a complex way to produce a rich, rasping
sound. All acoustic (non-electric) string, wind, and
percussion instruments are played by plucking or
bowing, blowing, and striking.

STRING HARMONICS
Harmonics are the different
frequencies at which something can
vibrate. A string stretched between
two supports can vibrate so that
varying numbers of wavelengths fit
along the string. The wave with the
longest wavelength is called the
fundamental. Other vibradons have
shorter wavelengths and higher
frequencies. This progressive series
of frequencies is known as
harmonics. The proportion of
different harmonics gives an
instrument its individual sound.

Node

Antinode

Node

Us,'"

Fundamental harmonic

Second harmonic

Third harmonic

Piano ^

Piano keys are connected to
hammers that strike strings
when the keys are pressed.
The pianist can press
several keys at once to play
chords. Some combinations
of notes are pleasing to the
ear, but others are not. The
effect of combining notes to
make chords is called
musical harmony.

the strings
onto frets
shortens the
length.

Short pipes make
high-pitched notes.

Long pipes make
low-pitched notes.

TRUMPET

A trumpeter vibrates his or her lips to
make the air inside the tube resonate.
Trumpeters can play different notes by
changing lip tension and by opening and
closing valves that alter the length of the
tube. Long columns of air vibrate more
slowly and make lower-pitched notes than
shorter columns. Blowing harder makes the
sound louder.

SITAR

Each string of a stringed
instrument vibrates at its own
natural frequency. The frequency of
a string can be increased by shortening
the length, increasing the tension, and by
using a lighter string. In many stringed
instruments, vibrations are passed to the
body of the instrument, which resonates to
amplify the sound.

Pianists can use all
their fingers to play up
to ten notes at the

Hammers

Keys

Antinodes at either
end of an open pipe
are where the air
moves most.

Air does not
move at a node.

PIPES

The column of air inside a pipe vibrates
by stretching and compressing. There is
a point in the middle of the column
where the air does not move. This is
called the node. The air vibrates most at
the ends of the column. These areas
are called antinodes.

same time.

Turning the
changes the
tension of the
string.

186

SOUND AND LIGHT

Violins and violas produce sounds
in the same way. The strings are
usually scraped with a bow, but
they can also be plucked.

The conductor controls and guides
the orchestra by beating a rhythm
with his baton and by signalling to
the individual players.

larger stringed instruments -
cellos and double basses -
produce the lower-pitched sounds.

Orchestra

The combination of differently
pitched string, wind, and percussion
instruments in an orchestra produces
a huge variety of harmony and timbre.
It is a combination that has been
carefully planned - each group of
instruments has its own special part
to play in the performance of a
piece of music. An orchestra can
play so softly that it can only
just be heard, but when
everyone plays together
loudly, the sound
level can reach
100 dB.

Harp strings are
plucked to
produce sounds.

The woodwind section includes clarinets,
which have single reeds, oboes and
bassoons with double reeds, and flutes,
which do not
have a
reed
at all.

Brass instruments
include trumpets,
horns, trombones,
and tubas.

PYTHAGORAS

The Greek philosopher and
mathematician Pythagoras
(c. 582-500 b.c.) believed that
beauty and harmony could be
explained by numbers. He
recognized the mathematical
relationship between the pitch of
a sound and the length of a string
or pipe, or the size of a bell. He
discovered that halving the length
of a string doubles the frequency
of its fundamental vibration, and
raises the pitch by an octave.

MUSICAL SCALE
A scale is a sequence of notes of
increasing f requency that progresses
in a natural and pleasing way. The
note at the top of the scale has exactly
twice the frequency of the note at the
bottom. Two notes, one of which has
twice the frequency of the other, are
said to be separated by an octave.

Each note in
a scale is a
particular sound
frequency _

An octave

- 262 294 330 349 392 440 494 524

A tight skin makes a
high-pitched sound.
A loose skin makes
a lower-pitched
sound.

BANGING A DRUM

The regular beat and rhythm of percussion instruments, such
as drums, helps to give an overall structure and mood to the
music. Hitting the stretched drum skin makes it vibrate, but
exactly the right amount of force must be used to make
the instrument vibrate in the right way. A tighter
skin gives a higher pitch, in the same way as a
tighter string makes a higher note.

Find out more

Vibrations p.126
Measuring sound p.180
Loudness p.181
Making and hearing sound

p.182

Reflection and absorption
p.184

Factfinder p.412

187

SOUND AND LIGHT

Sound recording

JUST AS WORDS written on paper can be read again and again

Sounds are recorded
on a CD as tiny pits
that are detected
by a laser.

sounds can be recorded and replayed. All sound recordings store
sounds by making a copy of the sound waves. There are two types
of sound recording: analogue and digital. Analogue recordings
store sound wave patterns as a wavy line cut in a record or as
magnetic patterns on a strip of tape. Digital recordings convert
sound wave patterns into numbers that map the positions of all the
points on a sound wave before being recorded. These numbers are
stored as tiny pits on a compact disc (CD) or as magnetic patterns
on digital audio tape (DAT), and then converted —

back into sound by a microprocessor chip. \

The pits
are digits
in binary
numbers.

DIGITAL RECORDING
Sound is recorded on a CD as tiny pits pressed into
the surface of the flat disc. The pits are digits in
binary numbers. Each number is a measure of the
height of the sound wave at a given moment. As
the disc spins, the CD player’s beam scans the
surface. When the beam hits a flat part of the disc,
it is reflected to a photo-detector that changes the
light into electrical pulses. When the beam
\ strikes a pit, it is

\ ___ reflected away.

Electrical signals from the
microphone are fed to the
record head. Its magnetic field
arranges the particles
into a pattern.

Digital recordings
do not suffer
from hiss like
tapes, or j
scratches like j
records. j

Sound waves can be
recorded as a series of
numbers. Each number
gives the height of the
sound wave at a
particular instant.

TAPE RECORDING

The tape inside a cassette is coated with a layer of
oxide containing magnetic metals. On a blank tape,
the magnetic particles point in random directions,
but when a sound is recorded on the tape, the
particles are arranged in a pattern that changes in
step with the sound.

records mm

I .wft.iy

As the stylus in the pick-up head uT
of the record player runs in the 19
groove, it vibrates, following the
pattern of the sound waves. This
sets up electrical signals in the pick-up
head. On a stereo record, the patterns on
opposite sides of the groove
are slightly different,
so different sounds j
come from right-
and left-hand speakers.

Recording studio a

Recordings are made by mixing jm
sounds from different instru- JHj
ments and vocalists. There is no
need to record everything at once j|H
- the sound engineer can add
sounds one on top of the other. The ™
engineer mixes the sounds using
sliders on the mixing desks.

THOMAS EDISON

first sound recording in 1877
was of the words “Mary had a
little lamb...” spoken by
Thomas Edison (1847-1931)
into his phonograph. This
recorded sound by
scratching a groove in a wax
cylinder. It had no electrical
parts, and relied on the
mechanical vibrations of a
needle to record and
reproduce sounds.

Stylus in

pick-up head runs
in the groove.

Groove is more
than 400 m
(1312ft) long!

Find out more

Semimetai^s p.39
Magnetism p.154
Electromagnetism p. 156
Electronic sounds p.189

;

188

SOUND AND LIGHT

Electronic sounds

EVERY SINGLE SOUND we know, including the sounds of the
human voice, can be produced electronically by digital sound
technology. Electronic instruments can also create completely
new sounds. Acoustic instruments can be replaced by
synthesized sounds or by sound samples - recordings that can
be played forwards, backwards, at a different pitch, or
processed in various ways by computer. Echoes and
reverberation can also be added to sounds electronically. In
| fact, it is possible for one person working in a small
jproom with a keyboard and computer to produce

the sound of a whole orchestra.

Machine head
alters the tension
in the strings so
that they can be
k tuned.

Special effects

Electronic music and special effects are Jk
composed for radio and television in a
radiophonic workshop. In the early days
of broadcasting, the sounds of thunder
were made by shaking a large metal
sheet; and the sounds of horses’
hooves by tapping coconut •••
shells. Now these sounds can
be synthesized.

Pick-ups v
produce a V
small \
electrical
signal when
, the strings
vibrate.

The effects processor can
add echo, fuzz, or distortion
to the sound of the guitar.

The guitarist
controls the
signal

processing with
a foot pedal.

SYNTHESIZED SOUNDS
A synthesizer is a musical instrument used to
make sounds electronically. The Moog
synthesizer, which was designed and
developed by the American engineer
Robert Moog in the 1950s, played one
note at a time. Today’s digital
BKy synthesizers can produce very
My complex arrangements of sounds.
w Professor Stephen Hawking cannot
speak, but is able to communicate using a
computer that synthesizes speech.

The amplifier
amplifies the
signal from the
guitar to drive a
loudspeaker.

ELECTRIC GUITAR

An electric guitar actually makes little sound of its
own - the sound it produces is made possible by
electricity. Plucking the metal strings makes them
vibrate. These vibrations are changed into tiny
electrical signals in the pick-ups beneath the
strings. These signals are amplified and processed
to make the guitar sound clear
or fuzzy, harsh or sweet.

Words are entered into the computer
through the keyboard and spoken by
a synthesized voice.

With a MIDI link, a
computer can be
programmed to control
the sounds produced by
electronic instruments.

Computer

Sound is picked up by
a microphone.

SAMPLING

A sampler records natural sounds and
stores them digitally. When the sound is
played back, the numbers can be altered
to change the frequencies, and therefore
the pitch, of the original sound. A
sampler can even make a musical scale
from the sound of a dog barking.

Drum machine

Keyboard

MIDI SYSTEM
A Musical Instrument Digital
Interface (MIDI) system makes it
possible for a computer to trigger
instruments such as keyboards and
drum machines to make sounds
together or in sequence. This
means that composers using a
MIDI system can write film scores,
music for television, and pop
songs - without having to use a
band or an orchestra.

Find out more

Sound is played bagk
on a keyboard. .

Sounds are
stored digitally
in the sampler.

Computers p.173
Measuring sound p.180
Reflection and absorption
p.184

Musical sounds p.186
Sound recording p.188

189

SOUND AND LIGHT

Light

Light energy

Just by standing in sunlight, you can
feel the energy that light carries. It
heats-your body, and causes chemical
reactions which tan and burn skin.

WHAT IS LIGHT? It is something we see and use every day, but
do not often think about. Light is a form of energy. The energy
from the Sun powers all of life on Earth. Light travels very fast.

When we switch on a light bulb, light floods the room almost
instantly. Almost, but not quite; it is actually travelling at about
300,000 km (186,000 miles) per second. In fact, the speed of light
is the universal speed limit. Nothing can travel faster. Light
sometimes seems to act as a wave, but unlike sound waves or
water waves, it can travel through a vacuum. At other times, light
seems to act as if it were a stream of particles. Light usually comes
from hot objects - such as the Sun or flames - but it can be made
in other ways too. Electricity can give off light, and some chemical
reactions can too - such as those in a firefly which cause

it to glow in the dark.

When the laser beam
meets a mirror, it is
reflected, just like a
billiard ball bouncing off
the side of the table.

REFLECTION AND
REFRACTION
Light travels in a straight line
through empty space, but when it
meets an object, it changes
direction. Some surfaces, such as
mirrors, reflect light like a ball
bouncing off a hard surface. Other
materials, such as glass and water,
refract light. This means they slow
down the light beam, and deflect its
path (slightly change its direction).

When the laser beam meets
glass, it is refracted. Its path
is deflected as it travels into
the glass from the air.

Light sometimes
behaves as though it is
travelling in transverse

In empty space,
the light of a laser
beam travels in a
straight line.

Particles

or WAVES?

Isaac Newton (1642-1727)
thought that light was made of
microscopic particles resembling tiny
billiard balls. Dutch mathematician
Christiaan Huygens (1629-95)
suggested that light is a wave motion,
like sound or water waves. Modern
quantum theory describes how light
behaves in some ways like waves, but in
other ways like particles.

The light falling on each square metre
of the Earth’s surface could power ten
electric light bulbs. Solar power
stations harness this energy by using
mirrors to focus sunlight on to a
central receiver. This creates steam
which can then generate electricity.

Hot objects, such as
the hot filament of
this light bulb, give

Light

sometimes

behaves as
though it is made
up of a stream
of particles.

SOUND AND LIGHT

Photoelectric effect

If light is shone onto a metal, it can
knock electrons out oft metal atoms.
This principle, called the photoelectric
effect, is used in the photocells of a
solar-powered calculator, which can
generate electricity from light. But
increasing the intensity of the light
does not increase the speed of the
ejected electrons, it just increases their
number. This can only be explained
by thinking of light as little packets of
light energy called photons. When a
photon strikes an atom it gives its
energy to an electron, which flies out
of the atom. More photons knock out
more electrons.

Photons
„ of light

A photon gives its energy to an
electron in a silicon atom. The
electron flies out, and can join
with others to make an
electric current to show up the
numbers.

DIFFRACTION
AND INTERFERENCE
When a light beam passes
through a narrow slit, it
spreads out. The narrower
the slit, the wider the spread.
This is called diffraction. You
can see this effect if you squint
at street lamps through your
eyelashes. If two diffracted light
beams overlap, the pattern they
make can only be explained if light
is a wave made up of peaks and
troughs. In some places, two peaks
or two troughs will meet to form very
bright spots. In other places, a trough
will meet a peak; these cancel each
other out leaving darkness. This is
called interference.

SPEED OF LIGHT
Eight travels much too
fast to be measured with
an ordinary clock.

French physicist

Hippolyte Fizeau (1819-96) made an
experimental measurement of the speed of
light in 1849. He shone a light through a
toothed wheel towards a mirror 9 km (5.5 miles)
away. He speeded up the wheel until the
reflected light beam could be seen through the
gaps between teeth. Fizeau then knew that the
light had travelled to the mirror and back in the
time the wheel had turned by just one tooth.

A toothed wheel is rotated very-
fast so that the light beam
passes through one gap on its
outward journey, and can return
through the next gap.

QUANTUM THEORY

l The German physicist Max Planck
(1858-1947) was the first to
Isuggest that light is neither purely
a wave nor purely a particle, but
has a combination of both
properties. This theory was later
expanded by Albert Einstein. To
understand how light is reflected,
refracted, and diffracted, we need to
think of light as being like sound waves,
with both a wavelength and a frequency. But to
understand how atoms emit and absorb light, we must
think of light as a stream of particles called photons,
each carrying a certain amount of energy. This theory

is called quantum theory.

An atom is given energy _
which can “excite” an
electron, causing it to
jump into a higher
energy level.

____ When this excited

electron falls back
down into its original
energy level, a photon
of light is emitted.

The observer
speeds up the
wheel until a
continuous beam of
light can be seen.

Find out more

Energy sources p.134
Sound p.178
Electromagnetic
spectrum P.192
Sources of light p.193
Reflection p.194
Refraction p.196
Light and matter p.200

191

SOUND AND LIGHT

Electromagnetic Spectrum

JUST AS LIGHT TRAVELS IN WAVES, so also do other forms of energy
including radio waves, microwaves, and ultraviolet waves. These are all
electromagnetic waves. The total range of electromagnetic waves is
called the electromagnetic spectrum. The colours of the rainbow
form the only part of this spectrum that we can see. All the other
waves are invisible. Although all these waves travel at the speed of
light, each group of waves has a different wavelength and carries a
different amount of energy. Infrared, microwave, and radio waves
have a longer wavelength and carry less energy than visible light.
Ultraviolet, X-ray, and gamma rays have a shorter wavelength
and carry more energy.

GAMMA
RAYS

^ Gamma rays are
very penetrating. They carry lots
of energy and damage living cells
as they pass through. Gamma rays
are given out by the nuclei of
radioactive atoms in nuclear reactions

and explosions.

The Sun is a source
of electromagnetic
waves.

X-RAYS

X-rays have enough
energy to travel through a
considerable thickness of
material - including the human
body. On an X-ray photograph
the denser parts of the body
show up as shadows.

RADIO WAVES

The electromagnetic waves used to
broadcast radio and television have
wavelengths ranging from
hundreds of metres down to a few
tens of centimetres. The size of
the aerial needed to detect a
radio signal is closely related to
the wavelength.

Visible light is the
only part of the
electromagnetic
spectrum we can see.

MICROWAVES
Microwaves are the shortest of
the radio waves and are used to
transmit radar signals. Some
/ microwaves have the same

/ frequency as water molecules, and
/ can be used to cook moist food. The
energy of the microwaves is converted
into heat as the water molecules vibrate.

ULTRAVIOLET WAVES
Sunlight contains ultraviolet (UV)
rays. Small amounts of UV rays
are good for us, but large
amounts can be bad for our eyes
and cause skin cancer. It is these
waves that tan and burn fair skins.

JAMES CLERK MAXWELL

It was the Scottish physicist
James Clerk Maxwell (1831-79)
who formulated the equations of
electricity and magnetism that
predicted the existence of
electromagnetic waves.
Approximately 15 years after
Maxwell published his equations,
Heinrich Hertz first produced
and detected radio waves.

INFRARED WAVES
All warm objects give off infrared
rays. Special photographs taken
with infrared rays are called
thermographs. Each colour
represents a different skin
temperature, ranging from yellow
(hottest) through to blue (coldest)

Find out more

Radioactivity p.26
Crystals p.30
Radio p.164
Television p.166
Fact finder? A\Z

192

SOUND AND LIGHT

Sources of light

EVERY OBJECT IN THE UNIVERSE gives off electromagnetic waves - stars,
trees, and even our bodies. Most of the time these are invisible because their
frequency is below that of visible light. But if an object is heated, the frequency
of the radiation increases and visible light is produced. Objects start to glow dull
red at about 500°C (900°F). At 2,000°C (3,500°F)they are bright orange, while at
5,000°C (9,000°F) they glow white hot, emitting all the colours of the visible
spectrum. But it is not only hot objects that produce light. An electric current passed
through a gas excites electrons which then lose their extra energy as light. Chemicals
can also release light. The glowing patterns
along the bodies of some deep-sea fish are
produced by chemical reactions.

Solar spectrum

The surface temperature of the Sun is
5,500°C (10,000°F). At this temperature
all the colours of the visible spectrum
are produced. But atoms in the cooler
outer layers of the Sun’s atmosphere
absorb certain frequencies of the
sunlight as it passes through. This
causes dark lines on the solar
spectrum, which are known as the
Fraunhofer lines.

Different gases produce
different coloured lights. Neon,
for example,
always gives
out a red light.

EDISON’S LIGHT BULB
American inventor Thomas Edison
(1847-1931) made the first
practical electric light bulb in 1879.
He passed an electric current
through a carbon filament to heat
it so that it glowed brightly.

Modern bulbs have a tungsten
filament that heats up to about
3,000°C (5,500°F).

NEON LIGHTS
A glass tube filled with gas
produces light when an electric
current flows through it. This is
not because the gas is hot, but
because the electrons of the gas
are given energy that they lose by
emitting it as light.

Positions of the Fraunhofer
lines indicate which elements
are present in the Sun’s
atmosphere.

SPECTROMETER
A glass prism changes
the direction of
different colours of
light by varying
amounts. In this way it
can split a light mixture into a
spectrum. An instrument called a
spectrometer uses a prism to split
the light from a light source into a
spectrum. The wavelengths of light
in the spectrum show which
elements are present in the source.

GUSTAV KIRCHOFF

German physicist Gustav Kirchoff
(1824-87) studied light spectra
using the spectrometer he
developed with the chemist
Robert Bunsen. He observed that
individual atoms and molecules
emit certain colours only when
heated. Kirchoff realized that each
element produces a distinct
spectrum of coloured lines that can
be used to identify the element.

LEDs can
produce red,
orange,
yellow,
green
light.

LIGHT-EMITTING

DIODES

Many modern hi-fi systems
have a light-emitting diode
(LED) display. LEDs change
electrical energy into light energy
- they give out light when a
current flows through them.
LEDs are small, need only a
small current and last longer
than filament lamps.

LEDs are sometimes used in
displays in calculators, cash
registers, and digital clocks.

Find out more

Che

Ele

Noble gases p.48
:mical reactions

:CTRICITY SUPPLY P.

Colour p.202

p.52

160

193

SOUND AND LIGHT

Reflection

The image in a plane
mirror is laterally inverted.
This means that the right
side of the object appears
as the left side of the
image.

Mirror
image

Have you ever
noticed that the mirror
image of an object
appears to be as far
behind a plane (flat)
mirror as the object is in
front? But it is not a real
image; there is no light
coming from behind the
mirror - the reflected light just
travels to our eyes as if it had
come from an object where
the image is. This type of
image is called a virtual image.

Virtual
image is the
same size as the
object

We SEE SOME OBJECTS because they make
their own light - like the Sun or a light bulb. But
we can also see objects that do not give off their
own light. They reflect light - light rays bounce off
them. We see the Moon because it reflects the
Sun’s light. Gases are generally invisible because
they are too thin to scatter enough light to be seen.
But liquids and solids are clearly visible. The
appearance of an object depends both on the
amount of light it reflects and on the texture of its
surface. A smooth white surface, for example,
reflects more light than a rough dark one. If a
surface does not reflect any light at
all, it looks black.

Light

source

SPECUIjVR reflection

Light is reflected from a
smooth surface at a definite
angle. Specular reflection of
a laser beam produces a
bright spot on a screen.

Reflected image

TWO-WAY MIRRORS
A glass sheet reflects
about 5 per cent of the
light falling on it. The
other 95 per cent
passes through. If the
light is equally bright
on both sides, the
reflections look weak. But if it is dark on one side
and bright on the other, the bright side looks like a
mirror because there is no transmitted light
swamping the reflection. People on the bright side
can see themselves reflected. People on the dark
side can see through the glass to the other side.

^ Diffuse
reflection

DIFFUSE REFLECTION
Rough surfaces reflect
light diffusely - scattering
it in all directions. Diffuse
reflection of a laser beam
produces a fuzzy patch
of light on a screen.

Specular

reflection

^ Audience

Mirror

™ Light

GHOSTLY APPARITION —

A two-way mirror was used in 19th-century theatres to produce a ghostly
image. Light shining on a hidden actor was reflected from a mirror onto a
large sheet of angled glass, and then onto the stage. If the Stag^ was dark,
the audience could not see the glass. All they could see was the plwi tom
appearing and disappearing!

HENDRIK LORENTZ

The Dutch physicist
Hendrik Lorentz (1853-
1928) used James Clerk
Maxwell’s theory of
electromagnetic waves to
explain how light is
reflected. Light energy is
absorbed by electrons,
which then re-emit it at a
new angle. Lorentz’s theory
confirms the law of
reflection, which states that
the angle of reflection is
equal to the angle of
incidence.

SOUND AND LIGHT

TELESCOPE MIRRORS
The world’s largest optical telescopes
use a large concave (dish-shaped) A
mirror to collect the light from
distant stars. This curved mirror
catches parallel light rays in such
away that they are concentrated
to one point.

Image is
upside-
down,
real, and
reduced.

REAL IMAGE IN A CONCAVE MIRROR
A concave mirror can focus light from a
distant object to project an upside-down image
onto a screen. The size of the image depends
on the distance between the object and the
mirror. The nearer the object is to the mirror,
the larger the image becomes.

The large main mirror is a
concave mirror several
metres in diameter.

Light reflected from the concave
mirror is sent to a smaller mirror. This
smaller mirror reflects the light to a
camera that produces either a
photographic image or a television image.

Reflected waves
seem to come from a
point behind the
barrier.

DRIVING MIRROR
Driving mirrors are convex.
They are curved outwards like
the back of a spoon. Convex
mirrors reflect light to produce
an image that is always upright
and reduced (smaller). This is
useful if you want a wide field of
view, such as in a car driving
mirror. The driver can see
farther out of the sides than with
a flat mirror.

Barrier

Reflected
_ wave

Virtual waves

The way in which a plane mirror produces an
image can be demonstrated with water waves.
Think of the barrier as a plane mirror. When the
circular waves meet the barrier, they
— are reflected. These reflected

to come from a

NOVELTY MIRRORS

A curved fairground mirror
produces distorted images that
can be both scary and amusing.
In reality, it is the mirrors
themselves that are distorted.
Their concave and convex
surfaces make the mirrors
hollow in some places and
bumpy in others. A bumpy
convex surface makes things
look smaller. A hollow concave
surface magnifies. You may
appear to have a long thin
m body and short fat legs.

Other parts of you may be
upside-down.

waves appear
point behind the barrier. As
the waves do not really
come from this point, it is
called a virtual image.

Image is upright
and virtual, as
well as
- magnified.

SHAVING MIRROR

If you put your face close to a concave mirror,
the light is reflected, producing a magnified
image of your face. But if you move further away
from the mirror, the image becomes confused
and then reappears upside-down and reduced.
You can see the same effects by looking into
the curved surface of a shiny spoon.

Find out more

Electromagnetic spectrum
p.192

Lenses p.197

Optical instruments p.198
Light and matter p.200

195

SOUND AND LIGHT

Refraction

- Angle of
incidence

Angle of
refraction

Light TRAVELS in straight lines. But when it passes from one
transparent material to another, the light rays bend. This is called
refraction, and is why a straw standing in a glass of water looks bent at
the point where it enters the water. Refraction occurs because light
travels at different speeds in different materials. Refraction was first
investigated by a Dutch mathematician called Willebrord Snell in
1621. A number called the refractive index measures the amount a
light beam bends when it travels from one substance
to another. Relative to air, air has a refractive index
of 1, water 1.3, and most glass 1.5. Light is not bent
as much when it enters water as when it enters glass
because it is not slowed down as much.

Refractive index

A laser beam entering a glass
block at an angle (the angle of
incidence) is refracted because light
travels more slowly in glass than in air. A
number called the refractive index of a
material gives the relationship between
the two speeds. In this case, the speed of
light in air divided by the speed of light
in glass gives the refractive index of glass
as compared with air.

Truck

down

ALL CHANGE
When a truck’s
wheels move at
an angle from a
hard surface onto grass, the grass
slows down the wheels of the truck
on one side, causing the truck’s
path to bend. Light is refracted in
the same way when it travels from
air into glass.

Each fibre is a fine
strand of glass.

Internal
reflection
channels light along
the fibre even if it is bent or twisted.

Angle of
incidence equals
critical angle.

Angle of
incidence

Incident

beam

ENDOSCOPE
The principle of internal reflection is put to
good use in medicine. An endoscope is an
optical device for inspecting the inside of the
body without having to operate. It consists of a
bundle of flexible optical fibres. Light is
channelled along the fibres by internal
reflections. A doctor can insert an endoscope
down a patient’s throat to examine the
inside of the stomach.

Angle of

_ refraction

INTERNAL

REFLECTION

The glass block above shows how light is
refracted as it emerges from glass into air and its
speed increases. When the angle of incidence is
small, the beam emerges at a larger angle. But as
the angle of incidence increases (right), the light
beam becomes more and more refracted until, at
a certain angle of incidence called the critical
angle, the light is bent so much that it does not
emerge from the glass at all - it is reflected
inside. This is called internal reflection.

DIFFERENT DEPTHS
Have you ever noticed that pools and
ponds are always deeper than they look?
This is because light is refracted as it
leaves the water, making the bottom of
the pool appear closer than it really is.

You can see this effect in this glass of
water. Light rays are refracted in such a
way as to make the button look closer
than it really is.

The light beam
is internally
reflected.

Light from
distant
objects

Light rays from the
button are refracted
as they leave the
water. You see the
button as though the
light rays were
travelling in a straight
line.

Bent light
rays

Cool air
Warm air

MIRAGE

When light bends, it tricks us into
seeing things in the wrong place. A
mirage is caused by light refraction
in the atmosphere. Light travels
more quickly through the warmer
air near the ground than it does
through the cooler air above. Light
is refracted in a curved path,
producing a false image of a distant
object. Mirages are common in
deserts where the air is very hot.

Image

appears here

Find out more

UND AND LIGHT P.l

Reflection p.194
Colour p.202
Vision p.204
Fact finder? A \2

196

SOUND AND LIGHT

Lenses

Light source

r The FACT THAT LIGHT BENDS when it passes from

Concave lens Convex lens

Light rays
diverge

air to glass can be made to work to our advantage.
Lenses are specially shaped pieces of glass or
transparent plastic that focus light, produce images, and
magnify or reduce a scene by bending the light
travelling through them. A lens becomes steadily more
angled towards the edge and may be either thicker or
thinner at the centre than at the edge. The shape of
the lens means that light is bent either towards or
away from a single focus (point). Each of our eyes
has a natural lens. You are using yours now to
focus on these words.

FRESNEL LENS
French physicist Augustin
Fresnel (1788-1827) invented a
lens made from a series of glass
rings. Fresnel lenses are not
suitable for producing images
because they distort too much,
but they are good for
concentrating light beams. They
are often used in lighthouses,
car headlights, and projectors.

Magnified
virtual image

Thick and thin

A lens that is thicker in the middle than at Ught rays _

the edge is called a convex lens. A convex converge to

lens converges (brings together) parallel a focus

light rays to a focus after they have passed

through the lens. A lens that is thinner in

the middle is called a concave lens. This

kind of lens diverges (spreads out) parallel

light rays so that they appear to come from a

focal point on the other side of the lens.

MAGNIFYING GLASS
Objects look much bigger when
seen through the convex lens of
a magnify ing glass. Tracing the
path of light beams through the
lens shows how it produces a
magnified virtual image of an
object. The extent of the
magnification depends on the
focal length of the lens. The
thicker the lens, the shorter the
focal length. Lenses with shorter
focal lengths are more powerful.

Convex lens
magnifies image
on the slide

„ - -***
- - '

\Lens

SLIDE PROJECTOR
The convex lens in a
projector produces a magnified real image of the
slide. The image is real because light passes
through it and the image can be projected on a
screen. The image is inverted (upside-down), so
the slide must be put in upside-down to appear the
right way up on the screen.

Magnified

virtual

image

ANTONI VAN
LEEUWENHOEK

Dutchman Antoni
van Leeuwenhoek’s
(1632-1723) microscope
made it possible to study
bacteria and blood cells for
the first time. This simple
device was basically a
powerful lens made from a
glass bead mounted on a
metal plate.

Object

Find out more

Optii

Polymers p.100
Giass p.1 10

EAL INSTRUMENTS
Vision p.204
'iiotoc;raphyp.20i

p.198

SOUND AND LIGHT

Optical instruments

Mirror
reflects
light on to
specimen
above.

Different
strength
objective
lenses can be
swung into
position when
needed.

BINOCULARS
Binoculars consist of two
refracting telescopes. Each
contains an objective lens and
eyepiece to form an image that
appears much larger than the
object being viewed.

MICROSCOPE IMAGE
When a wasp’s wing is
magnified to 50 times its
original size, details of the
scales and veins are clearly
visible. This photograph was
taken through the lenses of a
compound microscope.

Many FASCINATING DISCOVERIES have been made
through the lens of an optical instrument. Even a simple
magnifying glass reveals many times more detail than we
can see with the naked eye. The more sophisticated
instruments - made with a combination of mirrors and
lenses - make it possible to study everything from the
tiniest living organisms to the most distant objects in
the Universe. Microscopes using light can magnify up
to 2,000 times. Telescopes can capture and analyse
light from objects a million times more distant than
any star we can see in the night sky.

Wasp at
actual size

Specimen
table

Compound microscope

A compound microscope magnifies in
two stages. Light from a mirror is
reflected up through the specimen
into the powerful objective lens,
which produces the first magnification.

The image produced by the objective
lens is then magnified again by the
eye lens, which acts as a simple
magnifying glass.

Scales

IMPORTANT TELESCOPES

HERSCHEL TELESCOPE
This 4.2 metre- (13 ft-) diameter
reflecting telescope, named after
William Herschel, has electronic
cameras and computers to record and
analyse starlight. It is situated in the
clear atmosphere of the mountains of
La Palma, one of the Canary Islands off
Africa’s northwest coast.

Concave

mirror

Objective
convex lens

REFRACTING
TELESCOPE
A ref racting telescope
has a large convex lens
that refracts the light to
form an upside-down image
of a distant object.

Eye lens
magnifies
image.

Light source

REFLECTING TELESCOPES
Most modern astronomical
telescopes are reflectors, with a
large concave mirror that collects
and concentrates light. A second
mirror reflects the light to the
eye lens or camera.

Second

mirror

A camera or
electronic light
detector is
often fitted to
the eyepiece.

1789 William Herschel telescope,
England, 1.23 m (4 ft) diameter.

1845 Lord Rosse telescope,
Ireland, 1.83 m (6 ft) diameter.

1917 Mount Wilson telescope,
California, USA, 2.54 m (8 ft)
diameter.

1948 Hale Reflector, Palomar,
California, USA, 5 m (16 ft)
diameter.

1976 Mount Semirodriki
telescope, CIS, 6 m (19.5 ft)
diameter.

1992 Keck telescope, Hawaii,

10 m (33 ft) diameter.

Find out more

STur

Tele

Teli

Reflection p.194
Refraction p.196
Lenses p.197

)Y OF ASTRONOMY I

SCOPES ON EARTH

^SCOPES IN SPACE P

>.296

p.297

.298

198

SOUND AND LIGHT

LASERS

Partially silvered mirror
reflects most light but lets
some light escape.

INDUSTRIAL-LASERS
High-power lasers cut through
thick steel sheets as easily as a hot
knife cuts through butter. Lasers
are also valuable for surveying,
because a laser beam travels in
such a precise straight line. The
course of the Channel Tunnel
between France and England was
plotted by laser.

Pencil beams of laser light are now familiar sights at rock

concerts. But as well as being used for entertainment, laser light is
used in many practical ways, including eye surgery, surveying,
cutting steel, carrying television and computer signals along optical
fibres, and for reading information from bar codes and compact
discs. The property of laser light that makes it so useful is its
coherence (regularity). Ordinary light waves are jumbled and
irregular, but laser light waves are all in step with each other - like
marching soldiers. They can be
directed in powerful beams
that are both much brighter
and more parallel than light
from any other source.

Laser light can b e produced by
feeding energy into solids,
liquids, or gases. The colour of
laser light depends on the
elements present in the material.

Laser
beam is
both powerful
and delicate.

Photon

IASER SURGERY
Surgeons can control laser beams
with great precision to make
delicate cuts in the surface of a
damaged eye or to burn cancer
cells from a tumour.

Helium-neon
laser emits
- red light.

SUPERMARKET CHECKOUT
The computerized information
contained in the bar code of your
shopping items is read by reflected
laser light. The lasers in bar code
readers are now made with
semiconductors. Semiconductor
lasers use much less power than
the helium-neon gas lasers which
were used in earlier machines.

THEODORE
MAIMAN

The idea for the
laser, which was
based on Albert
Einstein’s theories of
light, was developed by
Gordon Gould in 1957.
The first working laser was
built by Theodore Maiman (born
1927) in 1960. Maiman’s laser
generated laser light by energizing
a ruby crystal with light from a flash
tube. Although only a few centi¬
metres long, it worked very well.

THREE-
DIMENSIONAL IMAGES

An ordinary photograph is made by one set of light waves
being reflected from the object on to film. But because laser
light is so regular, it can be split into two to produce a three-
dimensional (3-D) image. One set of waves is reflected by
the object. The other set of waves arrives at the film from a
different direction without meeting the object. Where the
two sets of waves meet, an interference pattern is produced
which is recorded on film. When the hologram is lit in the
right way, a 3-D image is reproduced.

T ACUP Power

UiAOLIa supply

Laser stands for Light

Amplification by the Stimulated Emission of Radiation.
That is quite a mouthful! But what happens inside a
laser is easily understood. Energy from a flash tube or an
electric current excites atoms in the laser material. Some
of the atoms emit photons which then stimulate more
atoms to emit photons travelling in the same direction.
Photons bounce up and down between the mirrors at
either end of the tube.

A hologram is a 3-D picture
taken with laser light. You
can look around the
image to view it from
the side.

Find out more

CURI

Semimetals p.39
Noble gases p.48
Speed p.118

tF.NT ELECTRICITY 1

UND AND LIGHT P.l

Light p.l 90

p.148

.77

199

SOUND AND LIGHT

Light and matter

HAVE YOU EVER FELT THE HEAT given off by a tarmac road on
a sunny day? The dark tarmac absorbs the light energy falling on it,
and its temperature gradually rises. While black surfaces absorb
light, white surfaces reflect light and heat up more slowly in the
Sun. This is why light-coloured clothes are cooler than dark clothes
in hot weather. As well as being absorbed or reflected, light can also
be transmitted; it passes straight through transparent
materials such as glass. The way that an object (matter)
absorbs, reflects, or transmits light affects
the way it looks.

A transparent material
transmits most of the light
fainng on it. A little is
reflected, which is why
we can see the
surface of the glass.

La-

l .

A translucent
material
transmits light,
but the light is
scattered inside the
material. This gives the

material a milky appearance.

FLUORESCENCE.

Some chemicals absorb ultraviolet light
and then release the energy as visible
light. This is called fluorescence. These
chemicals can be used to create
“glowing” clothes, paints, crayons, and
even make-up. Washing powder
manufacturers put fluorescent
chemicals in detergents to help white
clothes appear even whiter in sunlight.

Light is reflected off the
shiny spoon at the
same angle as it
arrives.

Dust

particles

White

light

Blue sky

BLUE SKIES

Have you ever wondered
why the sky appears
blue? It looks blue
because tiny particles of
dust and water vapour in
the atmosphere scatter
the short wavelength
blue light from the Sun
more strongly than the
longer wavelength red
light. But when we look
towards the setting Sun,
we see the unscattered
red light.

Photochromic spectacle
lenses darken when they
are exposed to bright
sunshine.

PHOTOCHROMIC
GLASS

In dull light, photo¬
chromic glass is almost
transparent. But when it is exposed to
brighter light, it darkens. The light energy
changes the structure of some glass
molecules so that they absorb more light.
This process is reversible - away from bright
light, the glass clears.

Opaque, transparent,

AND TRANSLUCENT
Everyday materials respond to light
in different ways. Transparent
materials transmit nearly all the light
that falls on them. Other materials
are translucent. Although they
transmit light, the light is scattered in
all directions by tiny particles inside
the material. Opaque materials do
not transmit any light. They either
reflect it or absorb it.

Most materials
are opaque. They
do not transmit any light
and cast dark
shadows.

Vertically
polarized
light —

Horizontally
polarized
light -— '

POLARIZATION
Light waves are transverse. This
means that they vibrate at right
angles to the direction in
which they are travelling.
Polarizing sunglasses only
transmit light that is vibrating
vertically. By absorbing
horizontally polarized light,
they help to reduce glare.

Transmitted
light

Light is not
transmitted

Find out more

Sound p.178
Electromagnetic
spectrum p.192
Reflection p.194
Refraction p.196

200

SOUND AND LIGHT

SHADOWS ARE FORMED because light rays travel in straight
lines and cannot bend around opaque objects in their path. The
sharpness of a shadow depends on the light source. A point
i||j| (small, concentrated) source casts sharp shadows. An

extended (large) source casts fuzzy shadows. The Sun is
V almost a point source because it is so far away; the

W shadows it casts are quite sharp at the edges. A more

extended light source, such as a fluorescent tube, casts less i
i distinct shadows. Perhaps the most spectacular shadows of all &
are eclipses - the shadows cast by the Earth and the Moon on I
each other when they block the light from the Sun. I

SUNDIAI.

The shadow cast by a sundial
moves as the Sun appears to move
through the sky. The motion of the
shadow can be used to tell the
time. The first sundials, which
consisted of simple vertical poles,
were used more than 4,000 years
ago in China.

Shadows '

When the Sun is directly overhead, it does not cast a shadow. But
when it is lower in the sky, shadows lengthen and are much longer
than the objects producing them. There are two parts to the
shadow cast by the Sun - the umbra and the penumbra. The umbra
is the region where the object blocks all of the Sun’s light. The
penumbra is where the object blocks light coming from some i
parts of the Sun but not from others.

Penumbra: Sun
is partially

hidden ... _ *

Umbra:
Sun is fully
hidden.

SOLAR ECLIPSE

During an eclipse of the Sun, the Moon passes
between the Sun and the Earth, casting its
shadow on the Earth’s surface. At points lying in
the penumbra, the eclipse is partial, and the
Sun is only partly hidden. But in the
umbra, day becomes night for a few
minutes as the Sun disappears.

Penumbra

Umbra

Penumbra

Moon

LUNAR ECLIPSE
Sometimes the Earth passes
between the Sun and the Moon.
This is called a lunar eclipse. When
this happens, we see the Earth’s
shadow as it moves across the face
of the Moon. At the centre of the
eclipse, the Moon is blocked from
view for more than an hour.

Umbra

eclipse was a frightening
event. It seemed to early
civilizations that a monster
was swallowing the Sun.

But as science developed,
and astronomical records
were kept, it became clear
that the eclipses were regular
events that could be
predicted.

SOLAR

CORONA

During a total
eclipse, the
Sun’s atmosphere,
called the solar corona, is visible.

Scientists are able to study the
activity of the gases in the corona.
Prominences, which are normally
invisible because they are swamped
by sunlight, can be seen hanging
above the Sun’s surface.

Find out more

Light p.190

Light and matter p.200
Sun p.284
Moon p.288

Study of astronomy p.296

Shadows

201

SOUND AND LIGHT

White light is a mixture

Colour

Rainbow colours

The different colours that make up
white light can be seen when a beam of
light is split by a prism. The prism
refracts the different wavelengths by
different amounts, and disperses them
(spreads them out) into a spectrum so
that they can be seen. Red light is
refracted least, violet light the most.

Imagine a world in which everything was the “colour” of daylight -
white. Life would be very drab. Luckily, our world is colourful. Our eyes
are able to distinguish the different wavelengths of visible light as
different colours. Each wavelength of light, or combination of
wavelengths, is a particular colour. The longest wavelength that we can
see is red light, and the shortest wavelengths are blue and violet. If
equal amounts of all the wavelengths of light are mixed together,
the result is white light. Many animals cannot distinguish between
different wavelengths, so they live in a world in which
everything is colourless.

Light from the Sun is a mixture
of all wavelengths from long
wavelength red light to short
wavelength violet light.

Prism
splits white light into
its component colours.

White light contains all the
colours of the spectrum.

INTERFERENCE COLOURS
The brilliant colours you
sometimes see on bubbles
are caused by light
interference. White light
rays reflected from the inside
of the soap film travel slightly
further than those reflected
from the outside. The waves in
each ray interfere with each other
where they meet. Some colours cancel
each other out, while others combine to form
bands of colours on the surface of the bubble.

Bar is emitting waves
just within the red end of the
visible spectrum.

As the bar is heated more, the
hottest part of it turns yellow.

Magenta filter transmits red and
blue light but absorbs green.

Green filter transmits only the green
region. It absorbs red and blue regions.

FILTERS

A filter is a plastic sheet that
absorbs some colours but lets
others pass through. For example,
a green filter absorbs the red and
blue parts of the spectrum but
transmits the green region. A
magenta filter absorbs green light
and transmits red and blue.

White light
be made by adding
together just red, green,
and blue light.

Magenta

The bar is now emitting most colours
of the visible spectrum, which add
together to give white.

Cyan

COLOUR TEMPERATURE
All objects give out electromagnetic
waves. But they are often invisible to the
eye. Heating an object gives the waves
more energy, and they become shorter -
short enough for us to see. At first, the
heated steel bar above glows dull red. As
it gets hotter, it turns to yellow. At the
highest temperature, the bar gives out
most colours of the visible spectrum,
which mix together to give white.

COLOURED LIGHTS
Red, green, and blue are
known as the primary
colours: you can mix these
coloured lights together to make
almost any other colour. If red, green, and
blue lights are mixed together, we see them
as white light. Where two primary colours
overlap, they produce a secondary colour.
Red and blue make magenta. Red and green
make yellow. Green and blue make cyan.

Find out more

Elect

Soi

Light p.190

ROMAGNETIC SPEC
p.192

JRCES OF LIGHT P.l
'ECIAL EFFECTS P.2 (

iTRUM

193

202

SOUINl) AND LIGHT

Colour subtraction

Objects THAT DO NOT PRODUCE light themselves are

coloured by a process called “colour subtraction”. They subtract
(absorb) light from some parts of the visible spectrum but not
others. For example, a leaf looks green because it absorbs nearly
all the colours in sunlight except one - green, which it reflects.
Pigments and dyes are natural or artificial substances added to
paints and inks to give them colour. A red pigment absorbs
green and blue and reflects only red light. A blue pigment
absorbs red and green light and reflects blue. By taking away
colour, these substances actually

add colour to our world!

When the colour images are
printed on top of each other, a
full-colour picture is
reproduced.

Yellow

Cyan Black is treated as a

separate colour so that
text and outlines are
reproduced sharply.

Four-colour printing

All colour photographs and
illustrations are reproduced from
just four coloured inks - magenta,
cyan, yellow, and black. Mixing these
colours in different proportions
produces all the different colours you
can see. When a book or magazine is
prepared for printing, the colour images are
scanned to separate the four colours
photographically. The films are used to prepare a
printing plate for each colour.

Chameleon

NATURAL
PIGMENTATION
The chameleon has pigmented skin cells
that change size and shape to blend in
with the colour of the background. In this
way, it is excellently camouflaged when
danger threatens. Cuttlefish have evolved
a “language” based on patterns of colour
change that ripple across their bodies.

Cyan absorbs red
light, so it reflects
a mixture of blue
and green.

Yellow absorbs
blue light, so
reflects a mixture
of red and green.

Magenta absorbs
green light, so
reflects a
mixture of red
and blue.

MIXING PAINT

Colour mixing with paint works by
subtraction. Magenta, cyan, and yellow ink
absorb just one primary colour each from
white light. Mixing any two of these
colours produces a bright, primary-
coloured paint. Mixing all three colours
together produces black.

MUNSELL COLOUR TREE

If you have ever tried to match a
colour exactly, you know how
difficult it can be. Our eyes are
incredibly sensitive to very slight
colour differences. In fact, we can
probably distinguish more than
10,000,000 various shades! The
Munsell colour tree is a system of
grading colours. The hue (basic
colour), chroma (amount of colour),
and value (lightness or darkness) are
measured. Each colour is then put in
position on the tree. Hue is shown by
its place on the circumference;
chroma by its distance from the trunk,
and value by its position on the trunk.

red

light and absorb
all the other colours.

RED OR BI.ACK SHOES?

In blue
light, the red
pigment absorbs
the blue light.

The sneakers above appear red in
daylight or when lit by red light
because they reflect only red light

and absorb all the others. But
what happens when they are lit by
blue light? They look black
(above right). This is because the
red pigment in the sneakers
absorbs all the blue light and
there is no red light in the light
source to be reflected.

Find out more

Dye

Eleci

:s AND PIGMENTS P.

'ROMAGNETIC SPEC
p.192

Reflection p.194
Colour p.202

102

TRUM

203

SOUND AN1) LIGHT

Vision

Contact
. lens

The WAY THAT OUR EYES AND BRAIN work together to produce
images is incredibly sophisticated. Imagine building a robot that
could track a tiny baseball, hit at 160 km (100 miles) per hour into
the air and run across a field to make a one-handed catch. The robot
would need at least two eyes to see in three dimensions to judge the
distance to the ball. But most important of all would be the robot’s
brain - the computer that interprets the images that the eyes create.
When it comes to recognizing images, the human
brain is still far more powerful than even the
most powerful computers.

CONTACT I-ENSES
As an alternative to spectacles,
many people wear contact lenses -
thin lenses that fit over the cornea.
These correct vision defects in the
same way as conventional spec¬
tacles, but are virtually invisible.
Modern lenses are made from a
soft, almost jelly-like, material that
floats on the surface of the eye.

Retina

Light rays from
image travel to
the eye.

Optic

nerve

A concave lens
spreads out light rays
to correct short sight.

Image is
upside-down
because light rays
cross each other in the
eye. The brain interprets the
image so that we see it the
right way up.

The eye

The human eye is a tough ball filled with fluid
that sits in a bony socket. The cornea is the
transparent, protective surface of the eye. It also
focuses light. The iris controls the amount of
light passing through the pupil. It closes up the
pupil in bright light and opens it wide in dim
light. The lens helps to focus light on the retina,
which contains a layer of light-sensitive cells.
These send signals via the optic nerve to the
brain where they are
interpreted to build up r A
our view of the world, i -M

LONG AND SHORT SIGHT
Muscles change the shape of the lens to
focus light onto the retina. In long-
| sighted people, the muscles are unable to
J' make the lens strong enough; light rays
are focused behind the retina. In short¬
sighted people, the muscles cannot relax the
lens enough; light rays are focused in front of the
retina. Lenses can correct both these conditions.

A convex lens
concentrates
light rays to
correct long
sight.

OPTICAL ILLUSIONS

Much of the information we gather from an image is
based on our knowledge of how things should look. We
judge the distance to an object because we are familiar
with its size and know how big it should be at a certain
distance. But we can be fooled! An optical illusion
misleads us about the relative size or distance of an
object by placing it in an unexpected situation. The
two balls here look the same size,
but the one behind is a football,
the one in front, a golf ball.

Chess board
seen through
left eye

STEREO VISION
Having two eyes helps you to
judge the distance to an object
by giving you two view points.
If you look at your finger, first
through one eye and then
through the other, it seems
to move. The movement
^ gets bigger as you move

the finger closer to your
eyes. Our brains combine our
right- and left-eye views into a
single 3-D image.

Balls are about
2.7 metres
(9 ft) apart

Chess board
seen through
right eye

204

SOUND AND LIGHT

In bright sunlight, both rods
and cones are fully j
activated and colour
differences are clear.

Retina contains a layer of
light-sensitive cells called
rods and cones.

Only the rods are
stimulated in moonlight,
so we cannot see
colours.

Cone-shaped cells
detect different
' \ ..colours

Nerve
cells .

NIGHT AND DAY

Colour differences
arc clear in bright
sunlight because both
the rods and cones are
fully activated. In
moonlight, only the rods are
stimulated, so colour differences
are much less distinct.

RODS AND CONES \\

The retina contains two nC "Wk
kinds of light-sensitive cells - N—
rods and cones. You have about
6,000,000 cone cells and
120,000,000 rod cells in each eye. The
cone-shaped cells respond to bright
light and different light wavelengths, so
they enable us to see colours. The rod¬
shaped cells are sensitive to dim light,
but not to colour.

Rod-shaped
cells detect low
light levels

Loop of green dots

Yellow dot

Red dot

Conical

lens

A fly can see you
coming from any
direction!

Guidelines visible in
ultraviolet
light.

Facet

INSECT’S-EYE VIEW 9
Insect eyes are sensitive to a 9
different part of the %
electromagnetic spectrum from the 1
human eye. Insects can see M
ultraviolet radiation that we JH
cannot detect. Some flowers w
have evolved with pigments that

are visible only in ultraviolet ^
light. These form guidelines that
direct bees to the centre of a flower to
find nectar.

COMPOUND EYES

The reason it is so \ \

difficult to swat a fly is NAiniufl* 8

because it has hundreds of eyes! Each
of its compound eyes is made up of
hundreds of individual facets (eyes) facing
in all directions. Each facet consists of a lens at
the surface with a second conical lens inside.
These focus and direct the light to the optic
nerve and brain.

SIMPLE EYE
("lams have a row of simple eyes
that are little more than pinhole
cameras. But they are sensitive to
light. They are able to detect the
motion of predators so that the clam
can snap shut until the danger has passed.

Find out more

Electromagnetic spectrum

p.192

Lenses p.197
Colour p.202
Photography p.206
Senses p.358

205

SOUND AND LIGHT

Photography

Dramatic NEWS PICTURES, holiday snapshots,
advertising and fashion photographs are so much part of
our lives that we take them for granted. But until the
19th century, the only way of recording a scene was to
draw or paint it. The discovery that the chemical
compound silver nitrate darkens when exposed to
light was made by a German doctor called Johann
Schulze in 1727. However, it was not until 1822 that
Frenchman Joseph Nicephore Niepce took the first
photograph. Early photographs appeared in
shades of dull, silvery grey, and could be seen
only from certain angles. But as with most
scientific discoveries, the principle was
worked on and improved by others.

Today, we can make electronic
photographs on computer disks with a
still-video camera. “Painting with
light” has come a long way!

Lens is made from
several pieces of
glass to reduce
distortions. The
glass elements are
coated with thin
transparent layers to
reduce unwanted
reflections.

CAMERA OBSCURA
The first cameras were based
on camera obscuras. These
were darkened rooms into
which an image of the
surrounding landscape was
projected through a lens.
Although entertaining, images
formed by camera obscuras
could not be recorded.

FILM FORMATS

Early photographs were recorded on metal or glass
plates. Today’s flexible plastic film is far more
versatile. It comes in a wide range of sizes and speeds
to suit different purposes. The speed of a film is a
measure of the amount of light that must fall on it for
correct exposure. Fast films work with short exposure
times, which means there is less danger of blurring the
image with camera shake. Slower films, however,
record more detail because they develop finer silver
grains when exposed.

Studio

photographers
use large format
film plates. These
record very sharp
images.

35 mm roll film is
the most popular
film format.

Ground

glass

focusing

screen

Shutter

The mirror
slips up
when the
shutter is
opened to
allow light onto
the film.

While the shutter is
closed, a mirror and a prism send
the light from the lens into the
viewfinder.

Camera

All cameras work by focusing the

correct amount of light onto a film to form an image. The
amount of light can be changed by adjusting the aperture -
a hole through which the light passes, and by altering the
exposure time - the time the shutter stays open to let
light through. Many cameras, such as this modern
Single Lens Reflex (SLR) camera, have built-in
photoelectric light meters that set the correct
combination of exposure time and
aperture automatically.

Pinhole

Light rays from ^
object travel in a
straight line through
the pinhole and onto
the screen.

PINHOLE CAMERA
The simplest possible camera
is a closed box with a small hole
instead of a lens. This lets light through
onto a screen at the back of the box. The
image can be quite fuzzy and long
exposure times are needed.

upside-down.

206

SOUND AND LIGHT

Darkroom

A film is coated with chemicals that
are sensitive to light, which is why
film developing and printing has
to be carried out in a
darkroom. Producing a black
and white photograph is a
two-stage process - each stage
consisting of several steps.

When print film is developed,
the result is a negative image.

This then has to be turned into
a positive image by printing it
on photographic paper.

DEVELOPING

PHOTOGRAPHY

LANDMARKS

1822 Joseph Nicephore Niepce
takes first photograph.

1839 Louis Daguerre takes first
photograph of a person.

1841 William Fox-Talbot invents
positive-negative process that
allows photographs to be copied.

1861 James Clerk Maxwell takes
the first colour photograph.

1888 George Eastman forms
Kodak company to market
flexible roll films and low-cost
box cameras.

1948 Edwin I.and markets the
Polaroid instant picture camera.

POLAROID FILM
A Polaroid film produces almost
instant pictures. When the exposed
film is pulled from the pack, rollers
squeeze chemicals onto the
surface of the film and the image
develops in about a minute. The
film itself has nine separate
layers, including three light-
sensitive layers. Cyan, yellow, and
magenta dyes spread through the
image as it develops.

COLOUR PROCESSING
Colour film works in a similar way
to black and white film, but the
film has three layers, each of which
is sensitive to either blue, green, or
red light. When the film is
processed, yellow, magenta, and
cyan dyes are added to the layers.
The result is a full-colour image.

Colour positive

Developer

Rollers

that fix the

ENLARGING AND PRINTING
After the negative has been rinsed
and dried, it can be printed. The
negative is placed in an enlarger.

Light is shone through the
negative, and a lens produces an
enlarged image on light-sensitive
paper. The print is then
developed and fixed in the same
way as the film.

Dark areas on negative
let less light through
than lighter areas.

JOSEPH NICEPHORE NIEPCE

The first photographic image was
produced by Joseph Nicephore
Niepce (1765-1833). He focused the
view from his window onto a pewter
sheet coated with light-sensitive
bitumen and left it for eight hours.
Niepce’s partner,

Louis Daguerre
(1787-1851) later
developed a
more sensitive
process (the
Daguerreotype),
requiring less
than a minute’s

exposure.

Chemicals

The exposed film is taken
out of its case and wound on
a reel. It is then immersed in
a tank containing chemicals
that develop the image. The
film is rinsed, after
which more
chemicals

image
are added.

Colour negative

COLOUR POSITIVE AND NEGATIVE
There are two kinds of colour film.

When a colour positive film is
processed, it reproduces the colours it
was exposed to and gives a colour
transparency or slide. When a colour
negative is printed, the result is a negative
image, which is then turned into a positive
image by printing it on photographic paper.

Lens

Film pack

Find out more

Tr,

\NSITION METALS P

Halogens p.46
Lenses p.197
Colour p.202
Vision p.204
Factfinder p.412

.36

207

SOUND AND LIGHT

Cinema

THE NOVELTY of being able to record images on film
was so exciting that people soon began looking for a
way to record moving images. The very first “movies”
were made by Thomas Edison in 1893. But these 15-
second films could only be seen by one person at a time
through a machine called a kinetoscope. Two French
brothers, Auguste and Louis Lumiere, were the first to
show a moving picture to an audience in 1895. Early
films were flickery, black and white, and silent. The first
Hollywood movie with a sound track was not shown
until 1927; colour movie film became available in the
1930s. Today’s filmakers not only have the
creative ability to tell a story, they '

also understand the science of ' •' ■ ?

sound and light.

^ Sound track is recorded as a wavy

line. Light shining through the sound /# g 1 V

track onto a photoelectric cell # | ' n . /

converts it into an electrical signal. UjjI flr C y/

Housing for carbon
arc lamp

CINE PROJECTOR
Intense white light is generated
when an electric current flows
across a small gap between two
carbon rods. A carbon arc lamp
in this 1950s cine projector
produced enough light to
project a bright image onto
a large screen.

CINE FILM

Cinema film, or “cine” film, is
actually a series of still
photographs taken rapidly one
after the other. A modern cine
camera takes 24 frames
(photographs) each second. When
the images are projected at the
same rate onto a screen, the
illusion of movement is created.

Image i s focused by
moving the lens
towards or away
from the film.

■V - Light is reflected from
the closed shutter and
then deflected by the
prism into the viewfinder so
that the camera operator can
see the image.

Cine camera

When the camera is

the shutter rotates

running,
opening and shutting 24 times a
second to expose each frame of the film in turn.
When the shutter is closed, a special mechanism
called a claw hooks into the slots at the edge of
the film and drags the next frame down into the
gate to be exposed. The jerky motion of the claw
and film makes the whirring noise you hear
whenever a film camera or a projector is working.

Zoetropes were
popular in the 19 th
__ century.

FILM EDITING
Many more minutes of film are
shot than are used in the final
movie - and they are never shot in
sequence! The film editor has to
assemble the individual shots and
link them together in the right
order so that the film tells a story.
This involves cutting up lengths of
film and sticking them together
with tape.

.... Image is made
up of red, green,
and blue
strips.

TV AND VIDEO

Movement on the
television and video screen
is created in just the same
v way as cinema film. Most
m televisions show a

complete picture 25
jM times every second. If
H you look at a television
ftt screen with a magni-

ZOETROPE
The zoetrope was a
slotted drum lined with images. As
it spun round, each picture was
seen for a fraction of a second
through a slot. If the drum spun
fast enough, the pictures merged
together and appeared to move.

Dots

combine to
form strips.

Find out more

Sot

Television p.166

JND RECORDING P. ]

Tight p.190
HOTOGRAPIIY P.20

[88

208

EARTH

evolution through time,

OLD IDEAS OF THE EARTH
Some Hindus, about 1,500 years ago, believed
that the world was supported on four elephants
standing on a giant turtle. Myths such as these
of how the Earth was created are part
of the tradition and early scientific thought of
any civilization. As technology advances, so does
our knowledge of how the Earth formed. Every new
investigation and analysis brings us closer to
understanding our planet and everything it contains.

EARLY MAP

The 15th and 16th centuries were a time of
exploration. Sailors set out from Europe to
find new lands, to expand trading empires,
and to circumnavigate (sail around) the
globe. The observations that they made, the
specimens they collected, and the tales that
they brought back provided the foundations
of the earliest understanding of the Earth.

A close look at minerals reveals
the chemistry of the Earth and
the different substances that are
produced by geological
processes. This is important in
mining. The study of minerals
is known as mineralogy.

Different types of minerals form different rocks. -
We use different kinds of rocks for buildings, for
road surfacing, or as raw materials for chemicals.
The study of rocks is known as petrology.

Earth science

Earth science includes the study of atoms and molecules in
geochemistry, and of galaxies in cosmology. In this century, a
vast range of information about the Earth has been collected
by geographers, geologists, oceanographers, climatologists,
astronomers, and so on. We are gradually relating all these new

facts to one another, building a

clear picture of the structure

Of ALL THE PLANETS that have been discovered so far, Earth is
the only one that contains life. From above, the Earth is seen as a
mass of land, sea, and air. Each of these is changeable depending
on the movement within Earth, and the energy from the Sun.

The study of the Earth is ongoing, and scientists are
constantly making new discoveries. The study of
geology was once known as the observation of
the rocks. However, during the late 20th
century, geology began to broaden to
the study of Earth and of all the
sciences that deal with
the Earth, known as
“Earth sciences”. This
incorporates parts of
modern technology,
chemistry, physics,
biology, and the
applied sciences.
Together, these
teach us about
the Earth.

Skyscrapers are built of stone removed from the
rocks, around frameworks of steel obtained from iron
ore, and windows of glass made from sand. Oil is
used to power the builders’ machines. The use of
geological principles to find usable materials is
known as economic geology.

This map of the
world is dated
Antwerpen, 1598

We must understand the
structure of the rocks to
discover how safe the
foundations are before sinking
our buildings into them, or
tunnelling through mountains.
The study of how rocks
move and change shape is
known as structural geology.

The location of farmland or towns
depends on the geography and
I and for ms of an area. The study of
landforms produced by the rocks and
their structures is known as
geomorphology.

We can compare the geology of our
home planet with that of our nearest
neighbours, and contrast their histories.
The study of the planets, including the
Earth, is known as planetology.

209

EARTH

FORMATION of the EARTH

Continental crust

Some new mountains
form as oceanic crust is
pulled down under a

In many places
the continental
crust continues
under the sea for
some distance,
forming a
continental shelf.

Flat areas of
continental crust
are formed when
deformed ancient
rocks are worn
smooth and covered
with sediments.

OCEANIC CRUST
The outermost layer of the Earth
that lies beneath the oceans is
called the oceanic crust. The
oldest parts of the crust are no
more than 200 million years old.
This crust is continually being
produced at ridges under the
ocean by volcanoes that push out
molten rock. Oceanic crust is
destroyed as it is pulled into deep
trenches. The ocean crust is made
up mainly of silica and magnesium
(or SIMA for short).

Oceanic crust

beginning to split apart,
it creates a rift valley,
as in Eastern Africa.

A series of
mountains forms
where two
continents collide.

Mountains such as the
Andes of South America are
formed by volcanic activity.

Ocean ridge

Volcanoes at ocean
ridges push out
molten rock.

I Ocean crust drawn down
under a continent melts to
produce volcanoes.

The molten rock
solidifies to form a
layer of dense rock.

The oceanic crust is
oldest and deepest away
from the ocean ridge.

CONTINENTAL CRUST
The outside layer of the Earth that forms
the land masses is called the continental
crust. It is older and thicker than oceanic
crust. Some of it has been submerged and
uplifted. Each continent’s complicated
history is shown by its structure and the
different kinds of rock it contains.
Continental crust is made up of mainly
silica and aluminium (or SIAL for short).

Lighter particles (silicates, for
example) are pulled on to the
outside of the heavy cores.
Very light gases may collect
to form an atmosphere.

ABOUND 5,000 MILLION YEARS AGO, the Earth
was no more than a spinning cloud of gas and dust
in space, part of a much, much bigger cloud. Most
of the material in this big cloud clumped together
at the centre to form the Sun. Across the rest of the
cloud, rings of material started to clump together
to form planets, one of which was the Earth. Like
all planets, the Earth has a layered structure, with
lighter material on the outside and heavier material
at the core. The original spin of the whole cloud is
seen in the way the Earth moves.

A flat shield area called a
continental platform is formed
because an area becomes covered

The Solar System
starts as a rotating
disc of gas and dust.

Heavy particles
of iron and
nickel sink to the
centre. Lighter
particles remain
on the outside.

The heaviest
particles of iron and
nickel attract each
other through gravity
to form the heavy
cores of planets.
Their large mass
produces a strong
force of gravity.

The first of two theories of how the Earth formed
is known as the homogeneous theory.

Particles of all sizes are drawn

Two THEORIES

Scientists are not quite sure just how a
swirling cloud of gas and dust solidified to
form the Earth. There are two theories. In
the first, the homogeneous theory, the
material that formed the Earth clumped
together, and then separated out into
different layers, with the lightest on the top.
In the second, the heterogeneous theory, the
core formed first from heavy materials, and
then lighter materials gathered around it.

The second theory of how the
Earth formed is known as the
heterogeneous theory.

The Solar
System starts as
a rotating disc of
gas and dust.

210

EARTH

Summer in the Northern Hemisphere is when
the North Pole points towards the
Sun. There is constant daylight
at the North Pole.

Meanwhile, the
Southern
Hemisphere

At springtime in the Northern
Hemisphere, the North and South
Poles receive the same
amount of sunshine, so
their days are the
same length.

SEASONS

. The Earth’s tilted
||k spin has a big effect on
■ - our lives; at certain times
|||p: of the year, the North Pole
yyy points away from the Sun; at
P other times, it points towards
the Sun. This produces
V changes in the climate that we
iff? call the seasons. Areas near the
W Equator are not so affected by
this tilt, so they have a more
constant climate.

TILTED SPIN
The Earth spins on an
imaginary line called its
axis, running between its
North and South Poles.
However, this axis is not a
vertical line. It is tilted, so
that the Earth orbits the
Sun at an angle

When it is autumn in the
Northern Hemisphere, it
is spring in the Southern
Hemisphere. Their days
are the same length.

Winter in the Northern
Hemisphere is when the North
Pole is pointing away from the Sun and is
in constant darkness. At the same time, the
Southern Hemisphere experiences summer.

Spinning earth

A planet’s Equator
is at 90° to its axis.

You might think you are standing still, but the Earth you are
standing on is continually spinning in space; it is not only
circling the Sun, but it is spinning on its own axis as well. A
year is the time the Earth takes to make one complete circuit
around the Sun. A day is the time the Earth takes to make
one complete turn on its axis. When the part of
Earth you are on is facing the Sun,
it is day; when it is facing away
from the Sun, it is night.

LONGER YEARS
The spin of Earth on its axis is
very, very gradually slowing
down. This is because of the
friction of the tides dragging
water back and forth around
the surface. From growth
lines on coral, scientists have
worked out that 400 million
years ago, a year was about
400 days long. This was
because the Earth was
spinning faster then, and so
produced shorter days.

The Earth spins around
its axis, which passes
through the North and
youth geographic Poles.

BULGING TUMMY
The Earth is not a perfect sphere
shape. It bulges slightly in the
middle. As the Earth spins, places
on the Equator move much
faster than places near the
Poles. The faster the
rotation, the stronger the
force, called the
centrifugal effect,
which pushes material
out from the centre of
rotation. This is what
happens when you
spin around, and your
hair is thrown
outwards. This means
the Earth is pushed out
most around its middle.

The diameter of the Earth from
pole to pole is 12,714 km
(7,900 miles). The diameter
through the Equator is just 43 km
(27 miles) longer. At the poles,
circumference (distance around
the Earth) is 40,008 km (24,860
miles); the circumference at the
Equator is 67 km (42 miles) longer.

It takes the Earth
approximately
365 days to orbit
the Sun.

The bulge around
the middle of
Earth will decrease
as the Earth’s spin
slows over the
next few thousand
9 million years.

The angle of
the Earth’s tilt
is about 23°.

Find out more

Roc

Origi]

Magnetism p.154
Structure of
THE EARTH P.212

KS AND MINERALS P

SI OF THE UNIVERSE

Earth p.287

.221
■ p.275

211

EARTH

Structure of the earth

The

mantle is
about 2,900 km
(1,800 miles) thick.

This lower part of the
mantle makes up the
greatest part of the
Earth. It consists of
stony materials formed
from silicate minerals.

The Earth’s only
liquid layer, the
outer core, is about
2,000 km (1,240 miles) thick.
It is made of iron, nickel, and
possibly other substances.

The solid inner core is about 1,370 km
(850 miles) from the Earth’s surface. It
is made of iron and nickel.

Layer upon layer

The Earth is made up of three main layers - the
crust, the mantle, and the core. The outer layer,
the crust, is a thin hard layer of rock. Heat from
within the Earth causes some of the rock in the
mantle to melt, whereas greater internal pressure
in layers below compresses the rock into a solid
state. The centre of the Earth, the core, has a
liquid metal outer layer, and a solid metal interior.

Neither S nor
waves are detected
here as they have all
been refracted (bent) by
the sudden change in
density between the
Earth’s mantle and core.

S waves cannot pass
through the liquid core
and are held back in this
region: only P waves
manage to get through.

An area
where no
waves can be
detected is known
as a shadow zone.

SEISMIC WAVES

Vibrations caused by an earthquake are known
as seismic waves and can be recorded by
sensitive equipment. Two types run though the
Earth’s interior: fast-moving primary (P) waves
and slower-moving secondary (S) waves. The
time delay between them can provide geologists

The Earth’s layers

The upper mantle is solid and
contains a soft layer called the
lithosphere. It differs
from the mantle
below in the type
of minerals it

When you peel an apple, you remove only a

thin, outer covering. Similarly, the surface of the
Earth is only a thin layer compared to what is below.
Because of the Earth’s immense size, drilling does not
reveal much of exactly what lies beneath. Instead,
other methods have been used to discover what is
inside the Earth. Most of what we know has come
from the study of earthquake vibrations that run
through the Earth. Over the years this has enabled
geologists to build up a picture of a multi-layered
Earth with a solid metal centre surrounded by
lighter materials. The more that is known about
the structure of the Earth, the more we are able
to understand about the way it works.

The Earth’s crust is about 6 km (4 miles)
thick under the oceans, and about 35 km
(22 miles) thick under the continents.

P waves detected in this area have
been refracted (bent) by the different
thickness of the
mantle and
the core.

Earthquake vibrations

P (primary,
pressure)
waves

The outer layer of the Earth is
made up of the crust and part
of the upper mantle; together,
these form the
lithosphere.

Focus of an

S (secondary,
shaking) waves

The deepest hole
in the world, when
compared to the
layers of the
Earth, gives an
idea of how thick
each layer is.

THE DEEPEST HOLE
In 1990 the deepest hole ever drilled
was in the Kola peninsula, in the
former U.S.S.R. It reached a depth of
12 km (7 miles) and is planned to go
down to 15 km (9 miles). But drilling
would have to continue for a further
6,355 km (3,947 miles) before the
centre of the Earth could be reached!

with valuable information about where the
waves originate. The waves refract (bend) when
they pass through different substances,
revealing changes within the Earth’s interior.

MOHO

The boundary between the crust and the
mantle is known as the Mohorovicic
discontinuity, or Moho for short. It is
named after Andrija Mohorovicic
(1857-1936), who discovered it in 1909.
Mohorovicic was born in Croatia, and was
a professor at Zagreb University. He
noticed that earthquake waves moved at
different velocities in the two layers.

212

EARTH

Earth’s magnetic field

Lines of magnetic force

Earth’s magnetism

The Earth acts in the same way as a huge magnet. A magnet
attracts certain materials towards it (such as iron) in an area
known as the magnetic field. Each magnet has two magnetic
poles. These are places around which magnetic materials
tend to concentrate. The Earth’s magnetic poles are situated
near the geographical North and South Poles. The Earth’s
magnetic field is known as the magnetosphere. This reaches
far out into space and protects our planet’s life from
harmful solar radiation. The magnetosphere is pulled into a
teardrop shape by the continuous stream of electrically
charged particles from the Sun, known as the solar wind.

Effects of solar wind on Earth's magnetic field

Invisible lines of
magnetic force are
drawn into and away
from the Earth's
magnetic poles.

Charged
particles
from the Sun

Some of the
particles are
drawn in towards
the poles.

The boundary of the magnetic field
is known as the magnetopause.

The solid inner
core rotates at a
different speed
from the rest of
the Earth.

Heat and pressure
within the Earth cause
the liquid outer core to

SOURCE OF MAGNETISM
Earth’s magnetism is thought to come from the way in
which the inner and outer core move. The solid
inner core moves at a different speed from
the rest of Earth. The magnetic field is
generated by the same forces involved
in the turning of an electric
motor. The convection
currents in the liquid are
also thought to have
an effect on its
magnetism.

The ancient temple of Rameses II

MAGNETIC REVERSAL

years ago

WILLIAM GILBERT

Queen Elizabeth I of
England’s physician,

William Gilbert (1544-
1603), first demonstrated
how the Earth acts as a
magnet. He did this using
magnetic compass needle.

Gilbert used compass needles,
which move up and down as well as

particles from the
Sun become trapped near the
geographic Poles; this creates the
glow known as the aurora borealis (northern
lights), or aurora australis (southern lights).

Polar reversals

volume of space
within the magnetic
field is known as the
magnetosphere.

The magnetotafl
is where the
magnetic field is
drawn away by
the solar wind.

The area where
the magnetic field
is compressed by
the solar wind is
called the bow
shock.

The Earth’s magnetic field varies constantly. On certain

from side to side to determine the

MAGNETIC BRICKS

When a rock solidifies, the direction of the
Earth’s magnetic field at that time is recorded
by its magnetic minerals and preserved. This
means that the magnetic field can be detected
in bricks baked 3,000 years ago, like those from
this ancient temple of Rameses II.

occasions, movement has been so dramatic that the
magnetic field has completely reversed itself, with the
North and South Poles changing place. This process is
known as polar reversal. It is not clear how this happens,
but we known that it has occurred about ten
times in the past three million years.

SPINNING TOP
A spinning top swings from side
to side when it spins about its
axis. The position of the north
magnetic pole is continually
moving in a similar way, and so
maps need to be updated every few
years. The magnetic pole differs
from the geographical Pole by
about 11 degrees - an angle known as
the declination.

magnetism at a point on the Earth,
and the geographic and
magnetic poles.

The axis of rotation is like
a vertical line that runs
down through the centre.

The top
spins about
its axis,
constantly
changing its position.

Find out more

Magnetism p.154
Formation of the earth p.210
Moving continents p.214
Rocks and minerals p.221
Record in the rocks p.226

213

EARTH

MOVING CONTINENTS

EARTH’S PLATES

The Earth’s surface is divided into a number
of plates, like the panels of a football. Each
plate is growing at one of its edges, moving
along, and then being destroyed at another.
The edge of a plate where it is growing is
called a constructive plate margin and these
lie along the ocean ridges. The edge of a
plate where it is being destroyed is called a
destructive plate margin and these lie along
the ocean trenches. The continents are
embedded in these plates and are carried
around by their movement.

If two continents collide and neither
can be subducted, they just wrinkle
up to form mountain ranges .,

50 million

years ago

Present day

Geologists call the large
land mass that existed millions
of years ago Pangaea.

INTERLOCKING CONTINENTS
Perhaps the most obvious sign that the continents are
moving is given by their shapes. The west coast of Africa and
the east coast of South America look like pieces of a jigsaw puzzle
that, if brought together, would fit snugly. This suggests that they were once
part of a larger continent that has broken up. This was noticed as early as
the 17th century, when mapmaking was becoming a more accurate science.

Plates collide,
pushing up
land to form
mountains.

A moving plate consists of the
ocean crust and the topmost
solid layer of the mantle.

Asthenosphere

An ocean ridge}
where new plate
material pushes up.

An ocean trench, where two plates meet. Old plate
material descends into the mantle and is melted. The
molten remains form volcanoes on the plate above.

World map of plates

African

Nazca

Eurasian

Arabian

Philippine

Pacific

Indo-

Austrahan

Pacific

Constructive margins

Antarctic

200 million years ago

' Destructive margins

For THOUSANDS OF YEARS, people believed that
the continents were fixed permanently into their
positions. Then, in the 1960s, the opposite was proven.
In fact, the continents are continually drifting around
the surface of the Earth like logs floating on a syrupy
sea. This is called continental drift. Also, the seabed is
being recycled every 200 million years; at certain sites
called ridges on the ocean floor, magma (molten rock)
is rising from inner layers of the Earth. It then
solidifies and moves outwards before being swallowed
up at sites called ocean trenches. Nowadays, this idea
of sea floor spreading is combined with the idea of
continental drift in a theory called plate tectonics.

Lithosphere

The Earth’s plates consist of the crust and
the topmost layer of the mantle. This layer
is called the lithosphere. Below this is a
layer of mantle called the asthenosphere,
which is quite soft, lubricating the
movement of the solid plates above. At
the ocean ridges, new crust is formed by
magma welling up through volcanic
action as the plates are pulled apart. The
ocean trenches are where two plates meet
and one is swallowed up (subducted)
beneath the other and destroyed.

F. Vine

D. Matthews

FREDERICK VINE AND
DRUMMOND MATTHEWS

Evidence for the movement of
continents is quite easy to find. But
finding tell-tale signs of sea floor
spreading is very difficult. In 1963, two
British geophysicists, Fred Vine and
rummond Matthews, were the first to
recognize the importance of one clue,
showed that the pattern of magnetic
stripes in the rocks of the ocean floor was
convincing evidence for sea floor spreading.

214

EARTH

The movement of continents

EVIDENCE FOR PANGAEA
How do we know that at one time the Earth
heldjust one continent? Because there is
lots of evidence to prove it. For example, j
geologists have found parts of the same
ancient mountain range on different
continents. Also, the same fossils have
been found scattered over the globe,
showing that the same animals existed
over one big supercontinent. ■

Fossils of a freshwater swimming reptile,
Mesosaurus braziliensis, have been found
in South Africa and Brazil.

PANGAEA

About 300 million

years ago, all the
continents came together to form a single
vast supercontinent that geologists call
Pangaea. This supercontinent existed
for about 100 million years. It then
began to split into two parts - a
northern section called I.aurasia, and a
southern section called Gondwanaland.

PRE-PANGAEA
Before Pangaea existed, the
landmasses of the world were in
separate continents. These
continents were scattered across the
globe, but were quite different from
those of today. Very slowly, they
were moving towards one another.

Future of the

CONTINENTS

About 200 million

years ago,

Pangaea began to break up, and
today’s continents split away. Ever
since, they have been moving at the
rate of a few centimetres per year
(about the same rate as your
fingernails grow). The position in
which the continents are today is just
a temporary one. A map of the world
of the future would be as strange to
us as a map of the world of the past.

In this “new
world”, Australia has
moved much further to
the north, and North
America has split away
from South America.

The way in which the
continents are moving
today has been ‘last-
forwarded” to create a map
of Earth in the far future.

FOSSIL EVIDENCE
Fossils of an animal called Mesosaurus
found in Brazil are identical to fossils
found in South Africa. But such an

MAGNETIG STRIPES
The rocks of the seabed
are magnetized in stripes; a
strip of rock magnetized
towards today’s magnetic
north lies parallel to a strip
magnetized in the opposite
direction. This pattern of
stripes is exactly the same
either side of the ocean
ridge. This is evidence of
seafloor spreading.

OCEAN FLOOR
The rocks close to the ocean
ridge are quite clean, because
they have had little time to
collect sediment. But farther
away from the ocean ridge, the
rocks are piled with thick layers
of sediment, showing the ocean
floor is older there. This is more
evidence of seafloor spreading.

animal could not have crossed the
Atlantic. This indicates that the animal
lived when America and Africa were
joined together. The continents moved
apart and the fossils were separated by
the Atlantic Ocean. Also, fossils of the
same plant and of the same age have
been found in South America, Africa,
India, Australia, and Antarctica.

This image shows
magnetic stripes in
each layer of the
ocean ridge.

When rock wells up from
the ridge, it is magnetized
towards the magnetic

Every few million years,
the Earth’s magnetic
field reverses; north
becomes south. Flocks
formed during this
period will have a
reversed magnetic
alignment.

COLUMBUS

In 1492, Italian-born explorer
Christopher Columbus
sailed across the Atlantic.

The voyage took him
70 days. The same
voyage today would
take him a little
longer. For today,

North America and
Europe are farther
apart - the Atlantic
ocean is 20 m (66 ft)
wider now than it was
500 years ago!

Columbus’ ship

Find out more

Forces p.114
Structure of the
earth P.212

Mountain building p.218
Seas and oceans p.234
Earth p.287

215

EARTH

Volcanoes

POMPEII

In a.d. 79, Mount Vesuvius erupted
and engulfed the Roman city of
Pompeii in hot ash. This covered
the bodies of victims and their pets.
When the bodies decayed, they left
hollows in the ground. These
hollows are filled with plaster to
make models of the victims.

Cauliflower-shaped clouds of
ash and dust are blasted into
the atmosphere, and cover
the surrounding landscape.

Andesitic volcano

An andesitic volcano is a steep-sided
cone. This forms as the melted
plate material comes exploding
out of the ground. The volcano
gradually builds up from the
slow-moving lava flows and
ash layers. The thick lava
it produces is called
andesite.

Imagine shaking and opening a can of fizzy drink. The pressure

that forces the liquid to spray out of the can is similar to the pressure that
causes a volcano to erupt. This violent explosion forms thick clouds of ash
and red-hot lava that spray out of the volcano and flow down its sides. The
eruption occurs when slabs of rock forming the Earth’s surface, called
plates, begin to move. When old plates collide, and one is ground down
beneath the next, the plates melt and produce very violent volcanoes.
Other types of volcanoes also exist, such as those that form as new plates
grow. The molten material wells from the mantle, spurting up as quiet
volcanoes. Some volcanoes lie away from the plate edges, above a very
active spot in the Earth’s mantle.

Nuee ardente
Jlowing down
the side of a
. 0 . mountain
0 New

Zealand,
August 1968.

NUEE ARDENTE

When the pressure in andesitic lava
is suddenly released at the surface,
it produces a nuee ardente . This is a
glowing cloud which causes an
avalanche containing a mixture of
gases, fragments of rock, and white-
hot ash. It crashes down the hill
slopes and valleys at speeds up to
100 km/h (62 mph), smothering
everything in its path.

World map of
volcanoes

The side of the mountain
collapses, releasing a
nuee ardente that rapidly
covers the countryside.

Mount Saint

Helens . USA

Yellowstone, USA

Andesitic lava often
becomes solid in the
volcanic vent. This
causes it to block the
vent. As the pressure
builds up, the volcano
may suddenly explode.

The volcanic vent
is shaped like a
funnel, partly filled
with ash from
previous eruptions.

A Andesitic volcano

Vesuvius, Italy

DISTRIBUTION
Andesitic volcanoes are named after the
Andes mountains where they were first
noticed. They are found in areas where
each of the Earth’s plates is swallowed up
beneath the next.

ANDESITIC ERUPTION
An active andesitic volcano is
extremely violent. The eruptions
can happen at any time and the
explosions cause considerable
damage. This type of eruption can
also send clouds of hot ash and
dust over great distances. The
image opposite is of an andesitic
volcano after the eruption.

In 1980,

Mount Saint

Helens in the

United

States, an

andesitic

volcano,

erupted,

destroying

miles of

forest.

216

EARTH

Plate moves
over hot

Volcano forms on the Chain of extinct
surface as rising volcanoes stretches

material breaks through, away across the ocean.

-—- i -—---

volcano is a
magma chamber,
a reservoir of
molten material,
that feeds the
eruption.

Fissure eruptions,
in which lava
rises through the
long cracks, are
common in
basaltic
volcanoes.

New Zealand

Molten lava flowing over rocks in Hawaii
LAVA SURFACES

Basaltic lava flows freely. Its cooling surface forms a
skin, which wrinkles and puckers with the movement
beneath. This ropy lava is known by its Hawaiian
name pahoehoe. If this surface breaks up, it forms
blocks of lava with rough surfaces, also known as aa.

MUD POOL

Water seeping through the ground
in a volcanic area may be heated by
the hot rocks beneath. The rocks
absorb volcanic gases, making them
acidic. The hot acid absorbed by the
rocks produces a sludge that comes
to the surface as a boiling mud
pool. The mud pools of Yellowstone
National Park in the United States
are popular tourist attractions.

Hawaii

Mount Fuji,
Japan

A Basaltic volcano

DISTRIBUTION

Basaltic volcanoes are found where the
mantle material rises up to form new plates.
They rarely appear above the sea surface. Hot
spot volcanoes, such as those in Hawaii, may
form a long way from the edge of the plate.

HOT SPOTS

Deep within the Earth’s
mantle are areas of great
heat and turbulence.
These are known as hot
spots. They create the
right conditions for
basaltic volcanoes to form
on the crust above.
Continuous plate
movement produces a
string of volcanoes.

HOT SPRINGS
Water from the ground heated by
volcanic rocks may come to the
surface as steaming hot springs.
Often a network of underground
chambers forms and if water turns
to steam in one of these, the
expansion pushes water up and out
at the surface. The reduced
pressure allows even more steam to
form, and the water is blasted
upwards, gushing out of the ground
as a boiling fountain called a geyser.

Basaltic volcano

Over areas such as hot spots, molten material
rises up from the mantle. If it breaks through
to the surface, it forms a dark runny lava
called basalt. Unlike andesitic lava, basaltic
lava usually flows for long distances
before solidifying. The resulting volcano
is broad and low, known as a shield
volcano. Most basaltic volcanoes lie
deep below the sea and the lava
that erupts into the water cools
quickly into blobs called pillow
lavas. On land, molten basalt
sprays into the air as a fire
fountain. The drops may solidify
in flight, forming volcanic bombs.

An exploding hot spot island in Hawaii

The great flow of lava from
basaltic eruptions solidifies and
builds up as flood basalts.

Find out more

Acids p.68

Moving continents p.214
Mountain building p.218
Earthquakes p.220
Rocks and minerals p.221
Mapping the Earth p.240

217

EARTH

MOUNTAIN BUILDING

Andes

MOUNTAIN DISTRIBUTION

East African block
mountains

World map of mountains Scottish Highlands

Urals

Himalayas

Like you, mountains also grow old, but not

so quickly. The vast Himalayan mountain range in Asia
began to grow 50 million years ago, but it is so young that
it is still being formed. Mountains are formed by the
forces of plate tectonics, movements that take place in
the Earth’s crust, pressing and squeezing against the
edges of continents. These forces thrust mountains out of
the Earth. Some ancient mountain ranges, such as the
Urals in Russia and the Scottish Highlands, mark where
continents collided at some time in the past. Great
stresses are involved in mountain building: look for the
twists and breaks of the rocks in mountainous areas.

An ocean plate slides beneath
a continent. The friction splits
the continental edge into
wedges, forcing each one
back beneath the next.

The major mountain ranges of the Earth are fold
mountains. These are formed by compression at the
edges of continents, or where continental plates have
collided. Block mountains, caused by stretching, are
less noticeable on the world scale. Volcanoes can be
formed among either fold or block mountains.

The pressure breaks
and crumples the rocks
well into the continent.

The broken continental
wedges produce islands
and rugged coastal
ranges. They consist of a
complex mixture of oceanic
sediments and continental material.

Fold mountain formation

Fold mountains are formed at the edge of a continent.
The continental plate crumples as it crashes into an
oceanic plate, which is forced beneath it. Islands and
sediments brought along by the oceanic plate become
plastered to the continent’s edge. These fold and force
their way up to become part of the mountain range.
The descending plate melts, and the liquid rises into
the base of the mountains, raising them further and
sending volcanoes to the surface.

Fold mountains: in theory

Fold mountains: in practice

Erosion carves the
rounded fold surfaces
into a jagged mess.

The gentle inland
folds wear down
(erode) into
steep slopes,
known as scarps
and vales.

With erosion

BLOCK MOUNTAIN FORMATION
The formation of new constructive
plates puts the Earth’s crust under
tension. This causes the crust to
split into blocks, separated by cracks
called faults. Some of these blocks
may subside, producing rift valleys,
leaving the upstanding blocks
between them as block mountains,
such as those found in East Africa.

Surface erosion
rounds off the
edges of the blocks
and covers the
faults. This can
make it difficult to
identify them.

Continental rocks
squeeze, crumple, and

Molten material rises from
the descending plate.

Mountain roots model

FLOATING MOUNTAINS

In 1855, G.B. Airy, the British
Astronomer Royal, suggested that
mountains behave like blocks of
wood floating in water. The
higher they are above the
surface, the deeper they must be
below it. Modern research shows
that the continental crust is far
thicker in mountainous areas
than in flat regions and that
mountains have deep roots
stretching down into the mantle.

Under tension, a
continent will split
into blocks that
move in relation to
each other.

Molten
rock pushes
through openings
to form andesitic
volcanoes. Granite is left
exposed at the surface.

Without

formed on the
coast, now far
from sea.

Block mountains

erosion

218

EARTH

Features of a typical fold

Thick beds of coarse rock, like
sandstone, crack as they fold,
forming joints. These fan out
from the fold axis. \

Formation of a fold

When beds of rock are subjected to such
pressures that they bend, the result is
called a fold. A fold that sags downwards
is a syncline, while one that arches
upwards is an anticline. These two are
usually found together. The
line along which the rock
' *****$^ bends is called the axis.

Beds of thin
layers, like shale,
crumple up when
they fold. ______

ly ™ ck

beds of
|r rock, like
limestone, may
be split by joints
parallel to the axis.

Competent 1 i I I |J j | { |

beds crack when they
are folded, but incompetent beds
deform and crumple.

TYPES OF FOLD
Rocks deform in different ways
producing different types of fold.
Those shown above are symmetrical,
which means that the plane that the
fold bends around is vertical. In
asymmetrical folds, the fold appears
to be tipping over because of the
pressure applied to it. The pressures
may become so great that the whole
bed cracks and becomes a thrust.

Asymmetrical fold

FOLD

This folded rock strata found in Newfoundland,
New Jersey, U.S.A., shows the shapes formed by
folds. A fold is recognizable in an outcrop by the

rounded shape it produces in the rock strata.

Recumbent fold

Thrust

When under
continuous
pressure, the
fold becomes
a thrust. This
can be seen
as either a fold
or a fault.

An asymmetrical fold
appears to lean. The
fold axes of each
bed are not directly
above one another.

A recumbent fold is
one that appears to
have fallen over itself.

Normal fault

The overhanging
block at the
surface soon
disappears by
erosion. s

—- A normal fault forms
by tension. Rocks
crack, and one slides
down against the next.

This rock found in Nikshahr, Iran, shows
both normal and reversed faults.

FAULT

A fault can be seen as a crack, with
the rocks at each side
displaced in relation
to each other. Thrust |

The block below is
separated from
the block above
by the fault plane.

The edges of the
beds are curled
against the
fault. This is |
known as a
drag.

SAN ANDREAS FAULT
The spectacular San Andreas fault
crosses the Carrizo Plain. It
stretches across 450 km (300 miles)
south of San Francisco and 160 km
(100 miles) north of Los Angeles.

It is an example of a seismic fault
and is responsible for some major
earthquakes in the United States.

A reverse fault is formed by
compression. One block moves
-- up in relation to the other.

Dextral strike slip fault

Thrusts are very
shallow reverse
faults that can
be found in
mountainous
areas.

J In a strike slip
fault, the
/ blocks move
sideways rather
than vertically.

Right- — zr
handed H
(dextral)

Types of faults ******* t .

Sometimes, usually under tension rather than
pressure, the rocks do not bend and fold.

Instead, they crack into blocks that are
moving in relation to each other or that have
moved in the past. This is called faulting. The
surface area on which the blocks slide past
each other is known as the fault plane.

Find out more

Pressure p.127
Structure of the
Earth p.212

Moving continents p.214
Weathering and erosion p.230
Factfinder p.414

In a sinistra!, or left-
handed, strike slip fault,
the opposite block has
moved to the left.

Sinistral strike
slip fault

219

EARTH

Earthquakes

World map of earthquake zones

Imagine the force used by two people to snap open a

Christmas cracker. Now imagine the much greater force
needed to snap open the layers of rock that make up the
Earth’s surface. Rocks do not bend or break easily. Tension,
caused by movement of Earth’s plates, builds up over the
years until the rocks can take the strain no longer. Suddenly
they crack and shift, sending out shock waves, and reducing
anything built on the surface to rubble. This is what we call
an earthquake. The shock of the initial earthquake may be
followed by a series of aftershocks over the next few days.
These fade as the rocks settle down into their new positions.

Deep earthquake Shallow earthquake

zones zones

EARTHQUAKE ZONES
Earthquakes, like volcanoes, are found
along the edges of the Earth’s plates.
Shallow earthquakes happen where the
plates actually meet on the surface, while
deeper earthquakes occur where one
plate is sliding down beneath another.

MERCALLI SCALE

An earthquake’s intensity, or the amount it
shakes, is measured on the Modified Mercalli
Intensity Scale. This scale is based on what is
seen and felt during an earthquake. It runs
from the very gentle tremor of point I, to
point XII, which can cause total destruction.
The point within the Earth where the
earthquake takes place is called the focus.
The greatest intensity is felt at the epicentre,
the point on the Earth’s surface just
above the focus.

At point II
on the
Mercalli
scale, the

earthquake shock is
slight. You would notice it only
if you were standing upstairs.

At point VI on the
Mercalli scale,
windows break,
heavy furniture is
moved, and chimney
pots and plaster
come tumbling down.

Mercalli scale

The greatest rock
movement takes
place at the focus.

Lines
called
isoseisms
connect the
points at which
earthquake shocks
are of equal intensity.

After an

Vertical reading

The spring supports the
weight of the seismometer.

The movement of the
rest of the room is
magnified.

The revolving drum
records the magnified
movement.

In earthquake zones, buildings are
designed to reduce the dangers. High
buildings should swing without breaking.
Low ones are made of lightweight materials.

Horizontal reading

The room shakes
while the weight
remains still.

The shaking is
magnified by
the leverage.

The movement is
recorded on a
rotating drum.

SEISMOMETER

The seismometer is an instrument that records
earthquakes. It contains a weight that is so
heavy that it remains still while everything else
shakes around it. The shaking is magnified by
levers and recorded on rotating drums.

RICHTER SCALE

The size, as opposed to the intensity,
of an earthquake is measured on the
Richter scale using a seismometer.
The scale was designed in 1935 by
American seismologist
C.F. Richter. Severe
earthquakes reach
a reading of 6 or
more, but
some have
reached 8.9.

Each figure
means a force
10 times that of the
number below it.

Even the best-designed
buildings will collapse in a
severe earthquake. Taller
buildings may survive better than
low ones, and fire and disease
are constant dangers afterwards.

TOTAL DESTRUCTION
At point XII on the Mercalli scale, destruction is
widespread. The ground moves in ripples like
waves in the sea. Objects are thrown into the
air. Buildings are completely destroyed. The
geography of an area is changed permanently,
but, luckily, few earthquakes are this severe.

Find out more

Forces and motion p.120
Vibrations p.126
Structure of the earth p.212
Moving continents p.214
Mountain building p.218
Fact finder? A\ 4

220

EARTH

The GROUND WE WALK ON, build on, and grow gardens on is
made of rock. All the rocks in the world are made up of chemicals
called minerals. Through a microscope, a rock shows that it is made
of crystals of different minerals all growing together like a mosaic.
Each mineral has its own chemical composition, and there are
usually no more than half a dozen types in each rock. Three types of
rock make up the Earth’s crust. Rocks are formed in three different
ways to produce igneous, metamorphic, and sedimentary rocks.
Igneous rocks form when molten magma cools and solidifies.
Metamorphic rocks form when a rock is chemically changed by heat
or pressure to form a new rock type. Sedimentary rocks form when
fragments of rocks and other debris are cemented together.

Grey quartz
crystals

Biotite granite

Pink

granite

ip. « DIFFERENT GRANITE
* " An I n some rocks, such as
j* ■ WL granite, the crystals of
^ mineral are big

Ji " enough to be seen
with the naked eye.

Granite consists of the
minerals quartz, feldspar,
and mica. The rock can be
pink or grey, depending on
what type of feldspar it contains.

Graphic granite

POI^ARIZED LIGHT
. When a slice of rock is viewed
' through a microscope fitted
wk with a single polarized filter
gS (a special filter that only lets
** through certain light waves),
W the individual minerals are
¥ mostly transparent. Some
may show a slight colour, and
a few, such as iron, show up as
completely opaque.

DOUBLE POIJVRIZED ROCK
When the same slice of rock is
viewed through two polarized
filters, the minerals show up in a
spectacular range of colours.
These colours change if the rock
is turned under a microscope.
The individual minerals
can be identified by
their appearance
and by their colour
changes.

Hematite,
iron ore

JEWELLERY
Some minerals are very
beautiful, and are used
to make jewellery.
Their value depends
on how popular and
rare they are.

Amethyst
crystals forming
a rim in the
geode jfj

HEMATITE

The ore minerals contain a metal
that can be removed quite easily.
Hematite is an iron ore. Iron is
both durable and flexible, and
can combine with other metals to
form an alloy. Its uses range from
being made into pairs of scissors
to industrial construction work.

MOHS’ SCALE

Minerals can be identified by
their hardness. A mineral that
can scratch another mineral must
be harder than the mineral it
scratches. Mohs’ scale of hardness
ranges from 1 to 10. Talc (the
softest) is 1, gypsum 2, calcite 3,
fluorite 4, apatite 5, orthoclase 6,
quartz 7, topaz 8, corundum 9, and
diamond 10 (the hardest).

Find out more

GEODE

Minerals may dissolve out of the
rock by water or by volcanic fluids
passing through it. The minerals
are then carried elsewhere. Those
that build up along the sides of a
hollow in the rock can produce a
geode (a group of crystals that
grow inside a cavity in a rock).

Bonding p.28
Cr\stals p.30
Elements p.31
Ceramics p.108

Structure of the earth p.212
Fact finder pA\ 5

Diamond

ROCKS and MINERALS

221

EARTH

IGNEOUS ROCKS

Basalt is formed
when lava from a
volcano cools on
the Earth's surface.

BASALT

A typical extrusive igneous
rock is basalt, formed from
lava. It is dense and dark,
because of the minerals it
contains, and fine-grained
because of its quick cooling.

Granite crystals
are large enough
to see without a
microscope.

When a candle burns, a runny wax is

formed that trickles down its side and solidifies.
Igneous rocks are formed in a similar way. The
rocks solidify from a mass of molten rock, such as
when a lava flow cools and hardens. Because of
the heat needed to form igneous rocks, they are
sometimes called “rocks of fire”. There are two
main types of igneous rock: extrusive and
intrusive. Extrusive types form when molten rock
comes to the surface and cools quickly, as with
lava. This gives a very fine-grained rock. Intrusive
rocks are those that have solidified underground,
cooling slowly to produce coarse-grained rocks.

GRANITE

Granite is an intrusive igneous rock.
There are several types of granite,
but all are light-coloured because of
the light-coloured minerals within
them. Granite takes much longer to
cool than basalt, forming larger
crystals that are easier to see.

Batholith

Molten material
pushes upwards,
or '“domes”, to
form a laccolith.

VOLCANIC DYKE
When molten material squeezes its
way into a crack and solidifies, it
produces a medium-grained
intrusive rock. It is usually harder
than the surrounding rocks, so after
erosion, this intrusion stands out as
a prominent landscape feature.

Formation

Molten material from the
Earth’s mantle forms an igneous
rock low in silica, such as basalt.
The molten material from the
Earth’s plates forms an igneous
rock that is high in silica, such as
granite, which solidifies in huge
masses called batholiths, and in
dome-shaped laccoliths. Or it
forms in cracks, making vertical
dykes or horizontal sills. It can
also burst through the surface.
The rock is only seen when
overlying rocks are worn away.

Igneous rock structures

Magma reaches the Earth's surface
through cracks in the bedding plane.

A volcano is formed when
magma forces its way
through a weak point in
the Earth's surface,
usually via a dyke.

After erosion

Find out more

Carbon p.40
Structure of

THE EARTH P.212

Volcanoes p.216
Rocks and minerals p.221
Factfinder p.415

Cedar-tree laccolith

Ring dyke

ROAD SURFACING

Igneous rocks tend to be
very hard. When broken
up, they make a good,
strong road-surfacing
material, especially when
coated with tar. This
prevents their silicate
minerals (feldspars)
from breaking down in
the atmosphere.

A road surface is often made by
adding granite chippings to hot tar.

Multiple dyke

A structure called
a neck stands
proud once the
surrounding
volcano has
been eroded.

222

EARTH

Sedimentary rocks

Conglomerate

CONGLOMERATE
Shingle from the beach becomes
the coarse clastic sedimentary
rock called conglomerate.

Other clastic sedimentary rocks
include sandstone - made
from layers of sand in deserts
or in sea beaches - and shale,
made f rom layers of mud.

YOU NEVER KNOW what you might find in a
sedimentary rock. Many rocks of this type are
made up of lots of other rocks, or even animal
remains, all stuck together. Sedimentary rocks are
built up from particles laid down as layers, or
beds, of sediment and later buried, compressed,
and cemented into a solid mass. There are three
types of sedimentary rock. Clastic sedimentary
rock is made of broken bits of pre-existing rocks.

Shingle pebble beaches ir i •,

Chemical sedimentary rock torms when salt and
other substances dissolved in water are separated
from the solution. And biogenic sedimentary
rock is built up from the remains of living things.

^ A lake or an isolated arm of the sea
evaporates. The dissolved salts
gradually become more concentrated
and are eventually deposited.

Clastic

sedimentary

rock

Rain and
weather break
down the
rocks exposed
on the land
into rubble.

Chemical

sedimentary

rock

The rocky
debris is
washed down to
the sea by rivers
and deposited there.

Shelly limestone

Biogenic

sedimentary rock

A coral reef is, itself, a
biogenic sedimentary
rock. Pieces broken from
it and spread over the
surrounding sea floor can
produce another reef.

Different ■ -

| layers of
i rock contain

minerals with /

different /

solubilities. Coral

reef debris

Rock salt *

LAYERS OF SEDIMENT
Sediments that eventually
become sedimentary rocks may [
cover whole sea floors or small
areas. Where two environments
meet, as when a river delta
runs into the sea, there is a
mixture of sediment types.

Formation

The process that turns the loose sediments lying on the bottom
of the sea or on a river bed into hard sedimentary rocks is
known as lithification. There are two stages: first, the layers that
continually build up on top of the bed compress it, squeezing
out the air pockets, and interlocking the particles. Later,
undergroundwater seeping through the rocks deposits minerals
- usually calcite or silica - as it goes. These minerals build up on
the sediment particles, cementing them
together into a solid mass.

Millions of years ago

_ _*

SHELLY LIMESTONE
Biogenic rocks are
made up of once-living
material. The shelly
limestone above is
made up of broken
seashells. Other
examples of biogenic
sedimentary rocks are
chalk and coal.

ROCK SALT

Seawater contains dissolved
minerals. When an area of sea dries
out, these minerals are deposited as
a layer on the bottom. Rock salt and
certain kinds of limestone are
typical chemical sedimentary rocks.

Deep-water mud and
clays are deposited
on the sea bottom.

Sand and silt from
the mouth of a river

Hard bed of
limestone produces
a prominent ridge.

TODAY

Once the sediments are
turned to sedimentary
rock, they may be lifted by
Earth movements and
exposed at the surface.
Harder rocks, like
sandstone or limestone,
may be resistant to
erosion while softer rocks,
like shale, may be quickly
worn away. This will form
a step-like landscape. This
process is continually
happening today.

Sandstone beds are
more resistant than
the shale beds.

BUILDING STONE

Bedding planes - the boundaries
between the individual beds of rock -
tend to make sedimentary rocks easy
to split and to work. The harder,
more thickly bedded sedimentary
rocks, such as sandstone and
limestone, are commonly used as
building materials.

Find out more

Crystals p.30
Mountain building p.218
Rocks and minerals p.221
Weathering

AND EROSION P.230
Rivers p.233

Brownstone house, New York City, U.S.A

223

EARTH

Metamorphic ROCKS

MARBLE

Marble is a type of thermal
metamorphic rock,
formed when heat is
applied to limestone. Its
smooth texture and
haphazard structure make
it an attractive building
and sculpting material. Its
colour can vary from white
to white streaked with
brown, red, green, or grey.

The composition of the rock changes; this
is known as metasomatis. This kind of
metamorphism is produced by hot fluids
moving from an igneous intrusion.

Marble

The metamorphic rock
mylonite forms from the
movement of a fault.

When you bake bread, you mix flour, yeast,

and water together and bake it in a hot oven. In a
similar way, heat and pressure from the overlying
rocks may change the nature of the rocks below.
This process is called metamorphosis, which
means “change”. There are two main types of
metamorphic rock. The most common is known
as regional (dynamic) metamorphic rock. This
type involves vast volumes, and lies at the heart of
mountain ranges and deep within the Earth’s
crust. The second kind of metamorphic rock is
known as thermal (contact) rock. It is produced
by heat from nearby igneous rock when the
rocks come into contact with each other,
and the volume involved may be no
more than a few centimetres.

Igneous
intrusion
provides heat
for thermal
metamorphism.

Thin layer
(auriole) of
thermal
metamorphic
rock around
the intrusion.

Area of greatest
pressure and
temperature in
mountain roots.

Slight metamorphism
gives only partial
crystallization of
some minerals.

Metamorphic
minerals aligned
according to the
direction of
- pressure.

Deep
metamorphic
rocks show
signs of
compression,
rather than
directed
stress.

Slate

Formation

Pressure and heat deep underground crush and bake
existing sedimentary and igneous rocks, to form
metamorphic rocks. These forces change the mineral
content of the rock, sometimes completely, as in the
case of gneiss, a high-grade metamorphic rock. The
importance of this change is the change in the
mineral composition that takes place in the solid
state. If the rocks just melt and solidify again, the
result is still an igneous rock. Regional metamorphic
rock is only exposed after millions of years of erosion.

The lower
continental crust is
made up of high-
grade regional
metamorphic rocks.

SIATE

Slate is dark grey, shiny, and splits
easily into thin slices, because of
the flat crystals of mica produced
in it by metamorphism. A low-
grade regional metamorphic rock,
it is formed from a fine-grained
rock such as shale.

Gneiss

SLATE IN USE

New materials have
largely seen the decline
of slate as a roofing
material and as a
chalkboard surface.
However, one important
property of slate is that its
flat mica crystals enable it
to be split easily.

Slate roof of a house in Britain

SCHIST

There are many varieties
of schist, a high-grade A
regional metamorphic
rock. None of the rock’s 1
original minerals are left
unchanged.

Find out more

GNEISS

Pronounced “nice”, this is the
highest grade of regional
metamorphic rock. The minerals
within it separate into distinct
bands. The rock breaks in all
directions, but not along the bands,
as in the case of schist and slate.

Changes of state p.20
Mountain building p.218
Igneous rocks p.222
Sedimentary rocks p.223
Weathering and erosion p.230
Factfinber P.415

224

EARTH

FOSSILS

FOOTPRINTS

A trace fossil is one that does not

contain parts of the original

creature, just the marks

that it made. These jjBBi 9

include dinosaur

footprints, such as

those opposite found H

in sandstone in

Connecticut, United .

States. Ancient dung is
sometimes preserved as I

fossils that geologists V- .•

call coprolites.

A FLOWER PRESSED between heavy books.

also do this by preserving plants and animals as
fossils. A fossil is any part of a once-living thing
preserved in a rock. It may be an entire body, a
single bone, or just a set of footprints. Fossils tell us
about life in the past and help us to date rocks and
past environments. They show how mammoths
walked the cold tundra wastes of the Ice Age a few
million years ago. Tens of millions of
^^^^^^vears before that, dinosaurs ruled,
and before then was

animals have left their remains

Leaves in shale may decay, leaving just a thin film of
the original carbon in the leaf’s shape. When this
happens to entire forests, it produces coal.

Sharks’ teeth are hard
and durable, so they
can be preserved
unaltered, unlike j

the rest of the J?

skeleton.

If the original remains decay
completely, they may leave a
h ole in the rock cal led a
BHfighk mould. If the mould
HH later fills with
sES minerals, it produces
H a fossil called a cast.

MARYANNING

Fossil enthusiast Mary Anning
(1799-1847) came from
Dorset, in southern
England. She became

Mould

one

of the most famous early
professional fossil collectors.

As children, she and her
brother Joseph found the first
complete skeleton of the
swimming reptile Ichthyosaurus.

Fossilized animals that evolved quickly, and
lived over a wide area, are the most useful
for dating rocks. Ammonites, octopus-like
animals that lived in coiled shells, are a good
example of such creatures.

Fossils are rarely found on their
own. More often, many are
preserved together as assemblages.
Fossil assemblages are useful in
giving us an insight into ancient
environments and how animals lived
and survived under such conditions.

SABRE-TOOTHED TIGER
When an entire skeleton is
preserved, a museum may mount it
and put it on public display. One
example is this fossilized skeleton
of a sabre-toothed tiger found in
the tar pits in Los Angeles,
California, United States.

Ammonites help
to date rocks.

89 million
years ago

Ammonites
in red chalk

97 my a

Fossil dating

Fossils can tell us how old a rock is. If
the rock contains a fossil of an animal
that we know only lived during a certain
period of time, the rock can be dated
from that period. When several datable
fossils are present in the rock, the
dating becomes more accurate. This is
because the rock would have formed
when all the age ranges overlapped.

Find out more

Carbon p.40

Rocks and minerals p.221
Sedimentary rocks p.223
Record in the rocks p.226
Weathering and erosion p.230
Factfinder p.415

Deshayesites Douvilleiceras Hoplites Scaphites Hamites
forbesi mammillatum dentatus equalis maximus

225

EARTH

Record in the rocks

Unconformity between rocks in the Grand Canyon,
Arizona, United States.

UNCONFORMITY

A break in a sequence of rocks is called an
unconformity. It happens when a layer of rock is
lifted into a mountain chain and erosion wears it
down to a flat surface. This is covered by sea, and
upper beds of rock are laid on top of it. A gap in
the record of the Earth’s history has been created.

The ROCKS YOU SEE around you today are filled with clues
from the past. Like pages in a book, they record much of the
history of the Earth. Since layers of sedimentary rock are laid
down one on top of the other, those at the bottom must be the
oldest. A geologist, working like a detective, can make a study
through these layers; each layer reveals the conditions under
which it must have been laid down. The-composition of a rock,
its structure, and the fossils it
contains all paint a picture of
a certain environment from
the far past. This study of
rocks is called stratigraphy, or
historical geology.

DESERT ENVIRONMENT

Rounded sand
grains show
that they
have been
polished by
wind. Their
red colour
is due to
iron oxide,
created by
dry desert air.

SEA FLOOR
ENVIRONMENT
If the sea is warm and shallow, and the currents
are gentle, the chemicals in sea water may
form a deposit on the seabed. This
will be mixed with the remains
of animals that live there.

Dinsosaur bones found in Utah, U.S.A.
FOSSILS IN ROCK
Some animals may only live in very
specific environmental conditions
- for example, in mud that is very
low in oxygen. Their presence as
fossils in a rock layer tell geologists
about the conditions under which
that rock formed.

Rock sequence

A sequence of rocks can be used to work out
the history of an area. If the column of rocks
has been undisturbed, the beds of rock at the
bottom will always be the oldest, and those at
the top will be the youngest - this is the
principle of superposition. The layers of rock
then represent periods of time that follow on
from one another. This example tells the
story of a shallow sea that was laden with sand
by a delta and eventually became a desert.

At the bottom is the
oldest rock - a
thick layer of
limestone (calcium
carbonate),
crammed full of
fossils of shells.
This indicates that
the area used to be
covered by sea.

CURRENT MARKS
S-shaped bedding (called
current marks) in a layer of
sandstone, show that the
sand was laid down in a
river. The changing
current in a river creates
sandy “tongues” that are
preserved.

Large scale current marks in
Wealden sandstones,
Sussex, England.

In a desert, the sand is carried
around and set down by the
wind to form sand dunes. The
corners of the grains of sand
are worn off. The iron they
contain combines with oxygen
to form a red colour.

When the shelly
animals that live
in the sea die,
their shells collect
on the sea floor (if
there are no
strong currents to
wash them away).

Calcium
carbonate,
dissolved in
the water,
precipitates out to
give a deposit of
fine white crystals
on the seabed.

The youngest rock
is a thick layer of
red sandstone. This
indicates a desert
environment.

The sandstone is cross-
bedded. This happens
when sand dunes moved
over one another.

Above the
limestone are
alternating thin
layers of soft shale
and hard grey
limestone, with
some beds of coal.

DELTA ENVIRONMENT
In a delta, the river channels bring
sand down to the sea, covering up
muddy sea deposits to form
islands on which plants grow.
These islands are only temporary
as the sea often sweeps back again.

Shale is formed
from mud,
sandstone from
sand banks, and
coal from the plants
that grew on the sand.

DISCOVERIES

1669 Danish mineralogist
Nicolaus Steno notes that
sedimentary rocks were laid
down in the sea and so the sea
level must always be changing.

1788 Scottish geologist James
Hutton realizes that
sedimentary rocks are formed
by erosion and deposition.

1830-33 British geologist Sir
Charles Lyell publishes
Principles of Geology which says
that factors influencing
landscape today have operated
throughout Earth’s history.

1915 German meteorologist
Alfred Wegener puts forward
the theory of continental drift.

226

EARTH

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Precambrian

QUATERNARY PERIOD
The time from 1.6 million years ago
to the present day is called the
Quaternary period, shown
left. During this time, the
Ice Age occurred, and
human beings evolved.

TERTIARY PERIOD
The time stretching from 65 million to
1.6 million years ago is called the Tertiary
period. This was the time when mammals and
birds evolved to take the place of the dinosaurs and
other great reptiles that had just become extinct.

Forests gave way to grasslands, and the climate became cooler.

JAMES HUTTON

Scotsman James Hutton (1726-97)
was a great historian of geology.

In 1795, he published Theory
of the Earth in which he
explained that the Earth’s
features have developed
over many years from
changes that are still
taking place today. He
thought that there was no
sign of Earth’s beginning,
nor an outlook for its end.

Geological time

The timing of events in Earth’s history
can be done in two ways. The most
useful way is comparative dating, in
which one event is placed either earlier
or later than another. The other way is
absolute dating, in which actual dates
are given to events. Absolute dating is
very difficult; any timescale produced
in this way tends to change with every
new piece of evidence.

GEOLOGICAL COLUMN
Just as we date human history by
naming periods after famous events,
such as the Pre-Columbian age, so
geological time is divided into periods
depending on the kind of life that
existed at that time. These periods are
grouped together into eras.

When a rock forms, it may contain
some radioactive elements.

Quaternary

Radio

active

mass

remaining

After a time, known as the half-life, half of the
amount of the radioactive element has decayed.

After a further half-life, half of
the remainder has decayed.

CRETACEOUS PERIOD
The Cretaceous period lasted from 135
million to 65 million years ago.
The Earth was home to the
great reptiles. Most of
the modern continents
had split away from
the large land mass
Pangaea; many were
flooded by shallow
chalk seas.

TRIASSIC AND JURASSIC PERIODS
The Triassic and Jurassic
periods stretched from 250
million to 135 million years
ago. Reptiles were beginning to
evolve on Earth. Pangaea
started to break up, and deserts
gave way to forests and swamps.

CARBONIFEROUS AND
PERMIAN PERIODS
These periods spanned from
355 million to 250 million
years ago. This was the time
when continents came
together to form one big
landmass, Pangaea. Forests
(which form today’s coal) grew
on deltas around the new
mountains, and deserts formed.

1/8

1/16

This carries on until less and less
of the radioactive element
f W\ remains in the rock. By
( f ) measuring this amount,
V y the age of the rock can
T be calculated.

DEVONIAN PERIOD
The Devonian period lasted
from 410 million to 355
million years ago.
Continents started
moving towards each
other. At this time, the
very first land animals,
such as insects and amphibians, existed,
and many fish swam in the seas.

0 1 2
RADIOACTIVE DATING
In most rocks, there are tiny amounts
of radioactive elements. Over the years,
these break down into more stable
elements. As scientists know the precise
rate at which they do this, the age of a
rock can be calculated from the
proportion of radioactive elements it
contains. The less it contains, the older
it is. This is a type of absolute dating.

3 4

Time (half lives)

ORDOVICIAN AND SILURIAN PERIODS
These periods spanned from 510 million to
410 million years ago. Sea life flourished at
this time, and the very first fish evolved. The
earliest land plants began to grow around
shorelines and estuaries.

CAMBRIAN PERIOD
The Cambrian period stretched from
570 million to 510 million years ago.
At this time, there was no life on
land, but all kinds of sea animals
existed. The animals with hard shells
formed many of today’s fossils.

PRECAMBRIAN PERIOD

This is the largest length of geological time, covering seven-
eighths of Earth’s history right up to 570 million years ago. It is
divided into the earlier Archaean period when there was no life,
and the later Proterozoic period, when life of some sort existed.

Find out more

Radioactivity p.26
Structure of the earth p.212
Rocks and minerals p.221
Fossils p.225
Weathering and
erosion P.230

227

EARTH

ICE and GLACIERS

A hanging valley is the
side valley left as the
U-shaped valley deepens.

Valley glacier

Glacier ice may start off smooth,
clean, and snow-covered, but it soon
breaks as it begins to move. It
becomes stained by the rock
fragments worn away from the valley
sides. At its lower end (its snout), the
glacier appears dirtier as once-buried
rocks appear on the surface. Gullies
and tunnels carved into the ice by the
meltwater (ice melting into water)
also make the ice look unclean.

Transverse
crevasse: a
crack in the ice as a
glacier moves over
an obstacle

Terminal
moraine left at
the end as a
glacier retreats

HAVE YOU EVER SQUEEZED some snow in your hands? It holds
together because the pressure of your hands has turned the snow
particles into ice crystals. The same thing happens when great
masses of snow build up on top of each other, compressing the
layers beneath. This may happen in a shady valley of a mountain
range, where the snow does not melt from one year to the next.
Snow compressed in a hollow forms a mass of ice, which moves
slowly downhill towards the lower slopes of the valley. This is
known as a glacier. On cold continents, the same thing
happens, and the ice builds up into an ice cap.

Lateral

moraine

along the Medial moraine

sides along the

middle, where
two moraines

Valley glacier

Bergschrund: a big
crevasse formed as the
glacier pulls away from
the headwall

Arete, a

Area of compacted snow,

Lake at 180 m (590 feet) in Valley of Velka Studena
Dolina, Czechoslovakia

AFTER THE GLACIER
A valley glacier exerts such pressure on its
base and sides that it wears them away. When
the ice eventually melts, the valley is seen to
be worn into a U-shape. This has vertical sides
and a flat bottom.

A glacier’s structure breaks
while coming down a steep
slope. This is called
an icefall.

Subglacial
moraine on
the bottom

Serac: a
pinnacle
where the
crevasses meet

Englacial moraine
embedded in the ice

This rock was
dropped in East
Greenland by a
glacier.

Ice cave, worn
out by meltwater

the surface as
ice melts

GLACIAL DEBRIS

The rocky material picked up, carried along, and
dropped by a glacier is called a moraine. This
may consist of mounds of clay, or gigantic
boulders that have been carried for many miles.
Much of the Northern Hemisphere landscape is
formed by moraine left behind after the Ice Age.

NORTHERN HEMISPHERE ICEBERG
When a glacier reaches the sea,
particularly along the Greenland coast,
tides and waves heave it up and down.
The strains exerted on it cause pieces
to break off and float away, forming
icebergs. This process of producing
icebergs is known as calving.

Movement
of waves and
tides exerts
pressure on the snout
of the glacier.

Kame, a delta formed
byr

Glacier flowing
into the sea

Glacier calves an iceberg:

228

EARTH

Permian

Carboniferous

Precambrian

Ice ages

At certain times in the Earth’s
history, the climate becomes so
cold that extensive ice sheets
are formed. Such periods
are called ice ages. The
most recent began about
1.6 million years ago, and
after warmer interludes,
ended around 10,000 years
ago. Others took place in the
distant past. There were four
in Precambrian times, one in
the Ordovician period, and
one in the Carboniferous
and early Permian periods.

Permo-Carboniferous ice age; glaciers covering
much of the Southern Hemisphere

Pennsylvanian
Mississippi
Devonian
Silurian

Jurassic; middle of the
age of dinosaurs, warm
stable climates

Ice age time line

Ordovician ice
age: affecting
what is now
the Sahara
desert

Cambrian,
a mild
phase

LOUIS AGASSIZ

The Swiss Louis Agassiz was the first
to recognize that an ice age had
taken place. He noted that
some landscape features in
Switzerland had been
produced by glaciers. He
also saw similar features in
Scotland, where there are
no glaciers. He deduced
that at one time Scotland

Louis Agassiz bad been

(1807-1873) covered in ice.

Cretaceous

Verangian,'
final phase of late
Precambrian ice age

Palaeocene, tropical forests
Eocene

Oligocene

Miocene, dry grasslands

Pliocene, climates cooling

Pleistocene ice age, the
most recent

Modern times

Pleistocene ice age world The world today

Sturtian,
middle phase
of late

Precambrian
ice age

Huronian;
earliest known
Precambrian ice
age, known from
evidence found in
Canada, southern
Africa, and India

Gnejso,
earliest
phase of
Precambrian
ice age

Ice cap

Ice sheet

In the far north and the far south, glaciers
build up over continental areas, forming
ice sheets or ice caps. These move
outwards rather than downhill as
valley glaciers do. The two main ice
sheets are the Antarctic ice cap
and the Greenland ice cap.

These make up about
90 per cent of the Earth’s
fresh water. Snow in the
centre of a land mass will
eventually find its way to
the edge as ice.

Valley glaciers formed as
ice cap moves
between
nunataks.

IAST ICE AGE

The Pleistocene ice age was very irregular. The
glaciers advanced and, a few thousand years
later, retreated again, giving an interglacial spell
with warmer climates than now. This cycle took
place about 20 times in the 1.6 million years of
the ice age. It may not be over. We mayjust be
living in another interglacial era.

Prevailing wind
direction

Mountain sticking
through, called a
nunatak

Moraine carried vast
distances by icebergs
and dropped on sea floor

Meltwater

streams

Lake of water
formed by
pressure

Elevation of the
ground without
the glacier

Elevation of the
ground with the
glacier

Bare rock kept
free of ice by
prevailing wind

as the valley
glaciers
reunite.

The weight of ice moved by
the tides absorbs a
significant fraction of the
world’s tidal energy.

Ice shelf forms, as ice caps float out to sea.

ICE CAP

The windswept surface of the ice
cap may be over a kilometre above
the bedrock. Because of global
warming, the Antarctic ice cap has
begun to melt in recent years, and
some European glaciers
are smaller.

Broad stable ice
sheet creeping
slowly out to sea

Broad, flat-
topped icebergs

SOUTHERN HEMISPHERE ICEBERG
The icebergs that form in the southern ocean,
broken off the ice shelves of Antarctica, are broad
and tabular (flat). They may be many hundreds of
kilometres long and exist for years before melting.
Often these are tracked by satellite to help build
up a picture of the world’s oceans.

Edge of the ice cap in Iceland

Find out more

Pressure p.127
Floating and sinking p.129
Weathering and erosion p.230
Rivers p.233
Seas and oceans p.234
Factfinder p.414

229

EARTH

Weathering and erosion

Effects of weathering and
erosion on rocks

Gi£*& ,.X : Xx

THE SUREACE OF THE EARTH is constantly changing. The
movement of the Earth’s plates pushes up mountains and
builds up continents. At the same time, these new surfaces are
worn back down again and ground to dust, in a process called
erosion. It can be caused by many agents, but the most
powerful one is that of the weather. There are two
.-- j types of weathering - physical and chemical.

B.& - - ~ Physical weathering is the buffeting of the

wind, the washing of the rain, and the pull
of gravity. An example of chemical
weathering is when the acids in
rainwater dissolve away rocks.

DERATION EFFECT
Desertsoil is a mixture of
fine dust, sand, and coarse
pebbles. Wind blows away the
fine material - a process
called deflation - leaving the
heavier pebbles, which
eventually form a continuous
crust. The erosion then stops.

ZEUGENS

Sand flung about by the wind causes
erosion. Exposed rocks are
sandblasted into unusual shapes and
polished smooth. Most erosion takes
place near the ground, producing
overhanging cliffs and top-heavy rock
structures called zeugens.

INSELBERGS

Rounded hills in dry regions, such as Uluru (Ayers Rock) in
Australia, have been eroded by a combination of physical
and chemical weathering. These are known as inselbergs.
Infrequent rain eats into the surface layers of the rock. The
hot days and cool nights cause daily expansion and
contraction, which eventually splits the surface.

Pancake rocks,
known as
zeugens, found
in Punakaiki,
South Island,
New Zealand

The resulting
pebble has
several flat,
polished
- faces.

SALTATION
Because of their weight, sand
particles are usually bounced
along close to the ground.
This process is called saltation
which means “leaping”. As a
result, most erosion occurs
within about 1 m (3 ft) of the
ground. Tall pinnacles of
rock are worn away at
the base, producing the
mushroom-shaped zeugens.

Desert winds

Sand flung about by the wind is the most
powerful erosional force in a desert. There
are few plants in desert areas, so the soil is
not held together by roots - nor is there
much moisture to stick the particles to one
another. The wind therefore easily picks up
the loose sand and hurls it around in
sandstorms. Rocks blasted by the sand are
worn down to sand themselves; this is used
by the wind for further erosion.

DREIKANTER

Pebbles lying on the ground receive
an intense blasting by sand. This
wears away one side quickly, causing
the pebble to overbalance. This
exposes another pebble face. The
result is a pebble that is polished flat
on several sides - called a
dreikanter. The larger pebbles that
are found on beaches or dry river
beds show this effect.

Formation of a
mushroom rock
by saltation

The arrows show the direction
in which the wind is blowing.

These arrows show
how high the wind
blows the sand and the
direction it travels in.

Rolling over, the
pebble exposes
a new face.

A pebble is blasted
on one side by a
strong wind.

When one side is
worn flat, the pebble

230

EARTH

CLINTS AND GRIKES
Calcite suffers from chemical
weathering. Where limestone is
exposed to rain, the calcite decays
on the surface and along cracks.
This process erodes the rock into
blocks called dints separated by
enlarged cracks called grikes.

ACID RAIN

The natural acids in rainwater come from dissolved
carbon dioxide. In built-up
the rain also contains acids
from dissolved industrial
gases, such as sulphur
dioxide, causing acid rain.

This increases the rate of
chemical weathering,
damaging buildings and
statues such as this stone
lion in Leeds, England.

Find out more

Acids p.68

Frost, df.w, and ice p.268
Weather watching p.272
Cycles in the
biosphere p.372
Deserts p.390

Sand dunes

The sand that is blown from loose
desert soil usually builds up into
heaps called dunes. Sand dunes
are moved along gradually by the
wind. Only about one-fifth of the
world's desert areas consist of
sand; in these areas the dunes can
form in many different ways.

BARCHAN DUNES

The most familiar type of dune is the crescent
dune or the barchan. These dunes are shaped
like a crescent. They form because the sand on
the two ends is
blown faster than
that in the middle.

Many of these
barchans together form
the typical sand and sea¬
like landscape seen in big
deserts, such as the Sahara.

The wind blows
up and around
an exposed
outcrop.

The head of the
dune forms as
the sand builds
up against the
obstacle.

Head and tail sand dune

Rocky
outcrops are common
in deserts, posing
obstacles to the wind.

Barchan

dune

The tail of the dune fills in the sheltered
area behind the obstacle.

The low sides of the
dune move faster
than the high
centre of
the dune.

Coastal sand

dunes

showing

typical

sand dune

structures

in England

Ridges of sand build
up parallel to
the wind
direction.

The sand is
carried along the
sides of the ridges
by the wind.

Seif dunes

Sand is

deposited by the
eddy on the sheltered
side of the dune.

HEAD AND TAIL DUNES
Head and tail dunes grow near an obstacle, such as a
shrub. Sand builds up in front of the obstacle and forms
a tail behind it. However, there are
different types; an advanced
dune, for example, may be
deposited some distance
before the
obstacle, and
wake dunes
may line up
at each
side.

Decomposed granite in Cornwall, England
ROTTING GRANITE
Minerals such as feldspars, one
of the constituents of granite, are
vulnerable to chemical weathering.
Once the feldspars react to the acid in
rainwater, the other minerals become
loose and the granite crumbles.

The wind is slowed
at the ridges by
friction, producing a
series of eddies.

The wind is fastest
and strongest where
it is channelled
along the troughs.

Clints and
grikes in The
Yorkshire
Dales,
England

Dunes called longitudinal, or
seif, dunes form as long ridges
parallel to the direction of the
wind. They are most obvious
in places where the sand is
being blown across bare rock.

FROST WEDGING

In cold climates, a type of physical weathering called frost
wedging is common. Water seeps into cracks in the rock; as
this water freezes, it expands and enlarges the cracks.
Eventually chunks of rock fall away and pile against the
mountainside as scree slopes, such as the one opposite in
Camp Pont, in the Antarctic peninsular.

Sand ridges build up from the
sand deposited in the eddies and
shifted by the wind.

231

EARTH

Soils

Horizon A, the
topsoil: this is
organically
rich, but some
minerals are
taken out by
groundwater.

Horizon B,
the subsoil:
this is less
organic, but
is rich in
minerals
brought
down from
the topsoil.

Horizon C,
the parent
rock: this it
broken and
weathered
into loose
chunks, and
contains no
organic
material.

Horizon D, ^
the

underlying
bedrock: the
mineral

content of the soil comes from this.

Horizon 0,
humus layer:
deposits of
plant material

Different layers of soil

Soil profile

Soil is formed in a number of layers.
Their sequence is called the soil profile.
The layers, also called horizons, show
the different things that go into making
a soil - from the decay of rocks to the
addition of material from living things.
Not all soils have the same horizons,
whose sizes vary from soil to soil.

When we look at a landscape, we usually see grass, plants,

exist. Soils vary from one place to
another, depending mainly on
the underlying rock.

Clay is a heavy soil
and water cannot
drain through it. It is
sticky and plastic
when wet, and can
contain many
nutrients.

Peat is a dark coloured
soil containing a large
proportion of humus that
comes from the partial
decay of bog plants. This
soil tends to retain water.

A sandy soil is light, and
water drains through it easily.
It only contains a small
amount of organic matter, and
so it is not very fertile.

Chalky soil is thin and
stony, and drains water
quickly. The organic
material it contains
decays quickly, and so
it contains only a small
amount of humus.

Arctic

landscape

A cloud forest in
Venezuela

SOIL THICKNESS
The depth of soil depends on a
number of factors, such as the
presence of a slope, where any
soil formed may be washed away,
and the nature of the bedrock.
Limestone, for example, erodes
more easily than sandstone, so it
produces more decay products.
But the most important factors
are the climate and the erosional
effect of the weather.

Hot climates encourage the Cold climates produce little
weathering of rock and the weathering, so Arctic soils
decay of organic matter, tend to be very thin.

and trees. Without soil, these would not exist. Soil is a complex
mixture of fresh and eroded rocky material, dissolved and
redeposited minerals, and the remains of once living things. These
components are mixed together by the burrowing of animals, the
pressure of plant roots, and the movement of water underground.

The type of soil, its chemical composition, and the nature of its
organic origin are all important to agriculture, and therefore to all

our lives. Many different types of soils

Small landslide in
the Pindus
mountains,
Greece

Soil creep on slope

The soil creep pulls over
the exposed ends of
rock strata.

SLOPES

Slopes are unstable because
gravity pulls anything on
them downwards. Any
change in the soil adds to this
downhill movement; the first
frost pushes the soil downhill;
raindrops dislodge particles
downhill, and soil expansion
caused by soaking takes soil
downhill. As a result, artificial
structures on a slope tend to lean,
and growing trees are distorted.

SOIL CREEP

Soil on a slope moves gradually downhill,
particle by particle - a process called soil
creep. Usually, the particles of
soil are bound together by
grass roots, forming rigid
slabs. These move downhill
as a series of step-like
structures called terracettes.
They are often used as
trackways by grazing
animals, such as sheep
and cows, increasing
the rate of erosion.

Weathered

blocks move

downhill

Roads

crack as the

underlying

moves.

Soil creep on the Chiltern Hills, England

Trees

are tilted but
try to grow

vertically, causing the
trunks to curve upwards.

Walls, telegraph poles, and
other artificial structures begin
to lean and eventually collapse.

Find out more

Organic chemistry p.41
Rocks and minerals p.221
Fossils p.225
Weathering
AND EROSION P.230
Climates p.244

232

EARTH

Rivers

FLOOD
Rivers are important to people
as a form of transport, as
supplies of drinking and
industrial waters, and as a
source of irrigation. But
they can also be a menace.

A sudden increase in
rainfall can produce floods
that destroy the towns and
cities that are built
alongside the rivers.

A flood in Bangladesh. The river carries
particles of sediment which give it its colour.

Rainwater falls to form pools of water, or sinks
into the soil and re-emerges as springs. This water is
channelled into valleys and hollows, eventually
forming the streams and rivers that flow down to the
sea. Flowing water helps shape the landscape. It
wears away the rocks of the mountains, redepositing
the debris on the plains and lowlands, and eventually
the floor of the sea. Most of the world’s greatest rivers
lie in tropical areas, where there is usually a constant
supply of water because of heavy tropical rainfall.

River formation -
First stage

Spring

Tributary

A V-shaped gorge is caused
by the vigorous erosion action
of the river cutting downwards ...

Waterfalls and rapids are ——.
caused by the river passing
over harder beds of rock.

Deep pools are eroded from the -
river bed by the swirling water and
stones bounced along the floor.

Second stage

A floodplain is formed by the deposition
of sediments brought down from the first
stage. Most deposition takes place at
times of flood.

River stages

A river has three stages. In its first
stage, it moves rapidly, cutting deep
into its bed, picking up rocky debris
and carrying it along. In its second stage,
if, slows down, depositing sediments as well
as continuing the erosion. In its third stage,
all its strength has gone, and all the
transported debris is dropped.

Irrigation on Play a
Del Ingles, Grand
Canaria,
Canary Isles

The meander is
the temporary
river loop. Its
position
changes by
erosion on the
outside and
deposition on
the inside.

Eventually the ledge will
be eroded down and
the waterfall will
become a rapid (a fast¬
flowing and turbulent
section of the river).

'A--,

. - ^ V

Erosion by a waterfall

Ledge of
harder rock

Position of
waterfall
before erosion

The deposition of
sediment is
carried beyond
the plunge pool.

Plunge pool

The river meanders back
and forth, wearing back the
surrounding hills.

River terraces are the
remains of old floodplains
formed when the
land was
— higher.

*wm

WATERFALL
A waterfall occurs when a
river pours over a ledge of
hard rock. The drop causes
the erosion of a plunge pool
at the bottom, undermining
the ledge. The ledge
collapses, and the new
waterfall forms over the
newly exposed outcrop.

Third stage

An ox-bow
lake is a cut-off
- meander.

IRRIGATION

Crops need water to grow. Often
the water from rivers is channelled
to feed crops - a system known as
irrigation. The early civilizations of
Ancient Egypt produced complex
irrigation systems fed from rivers
such as the Nile.

A delta is formed
when a river sheds a
large amount of its
sediment at the
mouth of the river.

HYDROELECTRIC POWER

The energy in moving water has been
harnessed throughout history.
Waterwheels once turned
machinery that ground
corn or worked looms.
i Today, water from dams
can turn turbines that
generate electricity for
whole communities.

Sashta dam, a hydroelectric power
station in Redding, California, U.S.A.

A levee is a bank of
sediment deposited
along the river bed
and sides.

Find out more

Water industry p.83
Generators p.159
Weathering
AND EROSION P.230
Shoreline p.236
Rain p.264

233

EARTH

Seas and oceans

World map of ocean ridges and trenches

Deep BENEATH THE OCEAN waves,

on the seabed, lies hidden land. There
are mountain ranges, deep trenches, and
vast open plains covering as much as two-
thirds of the Earth’s surface. The only way
we can see them is by using complicated
scientific equipment. The pattern of the
land on the ocean bed is caused by the
great movements of the Earth, called
plate tectonics. The vast ocean ridges
build up where new material is added to
the Earth’s plates. The deep underwater
trenches are where one plate is sucked
down under another and disappears.

East Pacific
Rise

Mid-Atlantic Ridge

Mariana Trench

Philippine Trench

Java Trench

Tonga Trench

South-east Indian Ridge

Peru-Chile

Trench

SEABED MAP

A few decades ago, the ocean
floor was a mystery. Then, in
the 1960s, scientists invented
instruments that could detect
shapes in the land from a
distance. Today’s maps of the
seabed are made using these
remote sensing images.

Island arc - volcanoes
Atlantic Indian Ridge along an ocean trench

Continental
rise - piles
of sediment
at the foot
of the
continental
slope

Ocean ridge - undersea mountains

Abyssal plain -
huge expanse of
flat seabed

Continental slope -
the edge of the
/ continental shelf

Ocean trench -
deep troughs in
the sea floor

Continental shelf -
underwater edges of
the continents

A coelacanth (Latimeria chalumnae)
found near the Comoros Islands

Ocean floor

FEATURES

Most of the ocean bed is an
enormous flat plain which lies
3-4 km (1-3 miles) below the sea’s
surface. From this, the tall mountainous
peaks of ocean ridges rise up to within 2 km
(1 mile) of the waves. Right down in the depths,
dark ocean trenches fall to 10 km (6 miles) and
more. Around the coast, where the land rises up to
form continents, the water is shallowest.

The lower
part of the
diagram
shows the
heights
and depths
in their
true scale.

hidden depths of the oceans.

The coelacanth is a fish that scientists
thought had been extinct for 200 million
years. In 1938, one was caught in the
ocean waters off Madagascar and they
have been caught there ever since. It is
easier for ancient animals to survive in the
ocean depths because living conditions
do not change much.

An atoll in the
Maldives

SMOKER COMMUNITY

Hot volcanic waters full of chemicals bubble up along the
ocean ridges, forming dark plumes called “black smokers”.
The chemicals support bacteria.

Animals that eat the bacteria
have evolved there, and
so have other animals
that eat them.

Creatures that have
never seen sunlight,
such as these Crustacea
and mussels, live in these

A coral reef
begins to grow
in the shallow
water around a
tropical island.

CORAL REEFS
Coral will only grow where the
water is clear, warm, and
shallow. The shores of small,
tropical islands are ideal. Each
coral organism makes a limy
shell that joins with others to
form a firm foundation on
which still more corals can grow.
In this way, vast shelves, called
reefs, build up to just below
the water surface.

When the island disappears
under the waves, it leaves a
ring, an atoll, of coral with a
lagoon in the centre.

Find out more

Chemistry of water p.75
Structure of

THE EARTH P.212

Rocks and minerals p.221
Waves, tides,

AND CURRENTS P.235

If the island sinks, the
coral keeps growing and
forms a barrier reef
separated from the island.

234

EARTH

WAVES, TIDES, and CURRENTS

World map of currents

OCEAN CURRENTS

The OCEANS NEVER STAND STILL. Local
winds push the surface of the sea into waves which
pound onto the shore. The tides wash in and out
of harbours twice a day, following the pull of the
Sun and the Moon. Winds sweep the surface of the
sea into great ocean currents. As the Earth spins,
the currents twist and flow in huge circles called
gyres. Warm water travels away from the Equator,
and cold water moves in to replace it. Winds that
blow over the sea carry warm or cool temperatures
to nearby land. Warm water from the Gulf Stream
helps keep western Europe warm in winter. Many
cold currents flow at depth under the warm ones,
sometimes in the opposite direction.

South Pacific
Gyre

Warm currents

Cool currents

South Atlantic
Gyre

Gulf Stream

North Atlantic Gyre

North Pacific
Gyre

TSUNAMI

The huge swirling currents in the
oceans are caused by prevailing
winds. The Trade Winds in the
South Pacific ocean sweep the
cold Peruvian current up the west
coast of South America.

Wind blowing over the
water surface pulls each
water particle over.

Lowest high tides

This giant wave is caused by an
undersea earthquake. Vibrations
rush through the ocean at hundreds
of kilometres an hour. When they
reach shallow waters they slow down
and build up into vast waves, at times
76 m (250 ft) tall. The
tsunami crashes onto
the shore, sweeping
away anything
in its way.

Damage after a tsunami in
Alaska, March 1964

The circles
spread below the
surface but die
out farther down.

At the beach, the
movement slows
down. The top part of
the circle falls down
and the wave breaks.

HOW DO WAVES MOVE?

When the wind brushes the surface of
the sea, it sends ripples through the
water. Although the waves travel vast
distances across the ocean, each water
particle only goes around in a circle.

Highest high tides

SUN, MOON, AND TIDES
The pull of the Moon makes the
water bulge into a high tide on
both sides of the Earth. As the
Earth spins, each place has a high
tide twice a day. The Sun pulls up
the water too, but not so strongly.
At one time of the month it adds to
the Moon’s pull. At another, it
fights against it.

The water
particles close
to the surface
continue to turn
over and over.

How THE TIDES WORK

Imagine a mother swinging her
child around in circles. As they
twirl, the mother’s skirt flies out
behind her. The child is like
the Moon circling the Earth.
The mother is like the Earth,
and her skirt is like the high
tide on the side of the Earth
facing away from the Moon.

Child swings round in big Mother swings in a smaller

Skirt flies out behind like water
flung away from the Moon.

Moon pulls out
a high tide on
the Earth just
beneath it.

Another high
tide forms on
the far side
because of the
Earth's spin.

When the Sun
and Moon line
up, the high
tides are very
high and the low
tides very low.

When the Sun
and the Moon
pull in different
directions, the
tides are not as
high and low.

Find out more

ClR

Roci

Ice

Weath

CULAR MOTION P.l

tCS AND MINERALS P
’ AND GLACIERS P.2

ERING AND EROSIO

Shoreline p.236
Universe p.274

.221

N p.230

235

EARTH

Shoreline

COASTLINE

The tremendous power of the sea
is demonstrated here on this rocky
coast at Kiwanda, Oregon, United
States. Rocks form the basis of our
landscape, but these are broken
down and worn away by the
continuous pounding of waves.

Waves erode any
cracks in the headland,
enlarging them into
sea caves.

Sea caves on both sides —
of a headland may
enlarge and join, to form
a natural arch.

With continued erosion, the roof of
the arch collapses, leaving one side
on its own as a stack.

Whenever you go paddling on a beach, you are standing

on the edge of the sea, but on the beginning of the shore. Every
piece of land has a shore, and each shore is unique. The features
of a shore are determined by many factors, such as the strong
winds, crashing waves, the temperature, climate, and the types of
rocks that exist there. Shores can change from being sandy to
rocky, or vice versa. The shoreline is shaped as the wind blows
across the ocean surface, transferring some of its energy to the
water. This energy is seen as waves that can travel for long
distances. The energy of the waves is weakened as they hit the
shoreline, but their destructive force can still wear away

headlands and cliffs.

Air compressed in a sea
cave may burst through the
roof, forming a blowhole
that releases water and air
^ as waves crash inside
the cave.

Headland erosion

Headlands are made up of hard rocks,
but even these are eventually worn away.

Waves approaching a headland curve around
it, attacking it from the sides. This creates caves
and arches, which are then further eroded.
Erosion occurs in two main ways. Rock is
damaged by stones flung up by the waves
(a process known as corrasion or attrition), or
cavitation may take place. In this process, cracks
in the rock are enlarged, as air
compressed by incoming water
expands when the water retreats.

RIAS W)

If land subsides (sinks), or the sea
level rises, coastal regions become
flooded. At the end of the last ice
age, ice caps melted in oceans
worldwide and raised the sea level.

Hills became islands, and river
valleys flooded, creating indented
coastlines with branching
inlets called rias.

Rias and estuaries in
Galicia, Spain

FJORDS

When glaciers melt, they often leave U-shaped valleys. On
the coast, rising sea levels flood these valleys, producing
long narrow inlets with vertical sides. Deposits of rocks and
other materials at the mouths of the valleys give the inlets
veryshallow entrances. Such inlets have the Norwegian
name fjords or fiords, meaning a narrow strip of sea

between steep cliffs.

The headland is eventually worn down,
first into caves, then into arches and
stacks (sides of arches that become
separated by water from the seashore).

Geiringerfjord, Norway
Gairloch, Scotland

Sy It Island, Germany

Oregon, U.S.A

Galicia, Spain

Geiringerfjord in Norway

World map of coastlines

CHANGING COASTLINES
The coastlines of the world do not
always stay the same. They can
change dramatically in a relatively
short time as waves wear away the
land and changing sea levels
submerge or expose coastal areas.

236

EARTH

Beach formation

Rocks worn away from headlands do not stay as rubble
for long. They are ground down by waves into shingle
(fragments of rock) and sand, dragged along the sea
floor, and eventually deposited in a fairly sheltered
place to form a beach. Even there, rock particles do not
stop moving. They are constantly picked up and moved
further by storm-generated waves, and the lightest
pieces are shifted about by wind. Because of this
continual movement, a winter beach may consist of
coarse pebbles, while the same beach in the summer
may be sandy. Today, special fences called
groynes help stop this process.

Beaches are made up of
sand and shingle and
continually change; shingle
is deposited by big waves
and sand is deposited in
quieter times.

Beach material
builds up
against a
groyne

Longshore drift
carries sand across a
bay or river
mouth, dropping
it to form a spit.

Beach material is drawn
away from the
sheltered side (lee)
of the groyne.

2. The wave
withdraws, and
the stone rolls
directly down the
sloping beach
with the water.

Storms wash shingle
up the beach and
deposit it as a berm
(ledge), which remains
until the next storm.

Fences called groynes,
bolted to beams sunk 2 m
(6 ft) down, are built out
into the sea to prevent
longshore drift.

Cha Bahar Makran, Iran

washes a stone diagonally up the beach.

MOVING BEACHES
Beach particles are continually
moved by the ebb and flow of waves
in a process called longshore drift.

As they reach the shore, waves wash
stones and sand grains backwards
and forwards, and may cause them to
drift along the beach to a new place.

A tombolo

in Cha

Bahar

Makran,

Iran

This map shows a few
examples of the different
types of coastlines
found around the
world. The colour
coding helps
identify each type.

A lowland beach in
Sylt Island, Germany

SAND SPITS

A sand spit forming outwards from
the land across a bay may go right
across to form a bar. If a spit forms
between an island and the shore, it
is give n the name tombolo.

SALT MARSHES
Areas of sand built up by
waves can be moved about
by wind to form dunes. The
dunes may cut off areas of
fresh or slightly salty
(brackish) water, which
then collect mud and
develop into salt marshes.

Sand spit

Waves slow down
around the end of a
spit, creating
a “hook

Longshore
drift is the
movement of sand and
shingle along the shoreline.

A saw-toothed coastline
results when sand builds up
against groynes.

Longshore drift

3. The next wave washes the stone
diagonally up the beach again. In
this way, the stone follows a zig¬
zag path parallel to the coast. This
movement is called longshore drift.

A raised beach in
Gairloch, Scotland

MAKING NEW LAND

The sea has the power to build

up as well as destroy land.

Eroded material deposited on
beaches increases the land area,
while lowering sea levels expose
land that was once submerged.

® RAISED BEACH
When land rises or the sea
level falls, the shoreline is
left high and dry. This is
known as a raised beach.
Many raised beaches formed
in northern Europe at the
end of the last ice age. As ice
melted, the land slowly
began to rise up.

- Find out more -

Rocks and minerals p.221
Weathering
AND EROSION P.230

Waves, tides,

AND CURRENTS P.235
Weather p.241

237

EARTH

Coal

World distribution of coal

The SUN’S ENERGY from millions of years ago has

been preserved in a rock called coal. The Sun makes
plants grow. If these plants are preserved under
pressure for millions of years, they form a solid - coal.
When coal is burned today, this ancient energy is
released as heat. Coal contains the element carbon -
wood contains about 50 per cent carbon; coal can
contain up to 90 per cent carbon. Most coal began to
form about 350 million years ago, during the
Carboniferous period. The huge
swampy forests that grew then are
preserved today as the world’s
main coal deposits.

Forests grow
well in swampy
conditions.

COAL MAP

Most of the world’s coal comes from deposits laid
down in the Carboniferous period, when the
Earth’s vegetation was most lush. However, some
important coal seams (deposits of coal) of northern
Europe are much younger, made of wood f rom the
early Tertiary period, about 40 million years ago.

Coal formation

As coal is a rock formed from the remains
of living things, it is called a biogenic
sedimentary rock. Millions of years ago,
forests died and were buried in swamps
before the wood had time to decay. As the
mud and sand of the swamps slowly turned
to stone, the make-up of the wood changed.

Its components were carbon, hydrogen, and
oxygen; the hydrogen and oxygen were removed,
leaving a concentrated deposit of carbon.

MINING COAL

Coal is extracted f rom the ground by
mining. If a coal seam emerges
at the ground surface, miners
can tunnel in horizontally.

This is a drift mine. More
often, a vertical tunnel is
needed to reach coal deep
underground. This is a shaft
mine. If the coal occurs near
the surface, the covering
layers of ground are stripped
off to reach the coal. This is
an open-cast mine. Here
extracted coal is being
stacked in Australia.

DANGEROUS MINES

The Industrial Revolution in Europe during the 18th
century depended on coal - it was vital as an energy
source. But mining coal was very dangerous. Even
children had to work down the mines in
appalling conditions. One safety device was
invented by a scientist named Humphry Davy.

The Davy safety lamp
detected when gases
in a mine reached a
dangerous level.

Davy lamp

PEAT

Before coal is formed, a fibrous
material called peat develops.
In fact, at this very minute, peat
is developing in all the bogs of
the world. It is sometimes used
for fuel and as a rich plant food.

As it loses its
oxygen, the
buried plant
material is
compressed
into the fibrous
material called peat.

Lignite

Sediments
continue to be
deposited that
compress the peat into
rock. More oxygen is
removed from the peat,
turning it into soft brown
coal, called lignite.

Bituminous coal

Eventually
the wood is
compressed
so much that
it becomes the
compact black
glossy coal called bituminous
coal. This is the most common
type of coal used by industry.

A peat
cutting site in
the Falkland
Islands

The trees eventually die, covered
with swamp material. This is
compressed into a layer.

Find out more

Or<

Strug

Sed

Carbon p.40
3ANIC chemistry I
!oal products i\9

rURE OF THE EARTi

IMENTARY ROCKS P.
Fact finder ?A\ A

>.41

il p.212
223

238

EARTH

Oil and gas

World distribution of oil and gas

Gas collects
above the oil.

What happened to all the tiny plants and animals
that died millions of years ago in the sea? They formed
oil - the oil that drives cars, runs factories, and is used
to make many useful chemicals. The animal matter that
gathers on a seabed is broken down slowly by bacteria.
This process gives off a gas called methane, or natural
gas. If the material left heats up, it breaks down into
light molecules called hydrocarbons that move through
the rocks and gather as oil. Although natural gas is a
by-product, the natural gas that is extracted from the
rocks in places such as the North Sea is actually a

breakdown product of coal.

OIL MAP

The oil in the main oilfields of the world comes
out of rocks that date from two periods in time:
the Ordovician-Devonian period (400 to 350
million years ago) and the Jurassic-Cretaceous
period (200 to 65 million years ago).

Impermeable rock that the oil cannot
travel through. Oil is trapped beneath it.

Porous rock that the
oil can travel through

Oil collects in a porous
rock cal led a reservoir
rock, where it is trapped.
Usually it is trapped by
impermeable rock that
will not let the oil pass.

Oil reservoir

Animal matter collected in the rocks
decays into oil droplets that float in
the groundwater below. Because they
are lighter than the groundwater,
the droplets float upwards through
pores in the rock, until they are
trapped by a layer that will not let
them pass - a cap rock. Here they
collect to form an oil reservoir.

One oi l trap occurs when
the reservoir rock is faulted
against another rock.

In a stratigraphic trap,
isolated beds of porous
rock are embedded in
impermeable rock. If
these beds are tilted, the
oil collects at one end.

ALTERNATIVE THEORY

Although most scientists agree that
oil has been made from living
things, there is a theory that it is
actually formed from metamorphic
rocks. This may be proved or
disproved by a borehole that is
currently being drilled into
I 1 metamorphic

P ; rocks in

^ Sweden.

■HK|& Siljan ring

Beds of salt may
bend under
pressure and rise
through the rocks
above, pushing
them into a dome.
Oil can gather in
this dome.

EXPLORATION RIGS
Possible oil reservoirs are
found by studying the surface
land and by a method called
remote sensing - sound
waves arc sent into the
Earth, and their
reflections are recorded.
However, the presence of
oil can only be proved by
drilling a hole into this
ground. This work is done
with a structure called an
exploration rig.

The oil rig floats low in
the water, so that it is
not affected by waves.

Workers on an exploration
rig in the North Sea

PRODUCTION PLATFORM
Once it has been proved that
a good amount of oil is
present, it is extracted by
means of a production
platf orm. This sends down
boreholes to the reservoir
rocks, pumps up the oil, and
channels it into pipelines or
into tankers that transport it
to a refinery.

Find out more

Organic chemistry p.41
Chemical industry p. 82
Gas products p.97
Oil products p.98
Seas and oceans p.234
Factfinder p.414

A jack-up rig is used in
fairly shallow waters. It
has legs that extend to
the sea floor.

A tension-leg rig is used
in deeper water. It floats
but is secured to the
seabed by tethers.

In very deep water,
ships are used. The oil
drill is put out through
a hole in the hull.

239

05 it

EARTH

MAPPING the EARTH

Landsat image of Peloponnesus in southern Greece

SATELLITE MAP
Modern space technology has
revolutionized cartography (map-making).
Maps are drawn from satellite
photographs, which show how the Earth
looks from space. Satellites are very
sensitive and can pick out details such as
types of crops grown in certain parts of the
world, and the heat given off by factories.

Map

A map is a picture designed to
show an area of the Earth’s
surface. There are many different
types of maps available. The
appearance and detail of each
map depends on what it will be
used for. Those used for route
finding, for example, may
emphasize the roads, showing
different types of road
represented by different symbols.
Political maps will concentrate on
boundaries and legal divisions.

Cylindrical projection

IMAGINE TRYING TO SEE the whole world at a glance. This is
what a map enables us to do. Without a map, it would be very
difficult to get an idea of what the Earth looks like. For thousands
of years, people have been creating maps to help them discover
their surroundings. As maps have become more sophisticated,
large-scale maps have been drawn that show geographical features,
such as mountains and rivers, using symbols. Mapping the whole
Earth, however, involves laying out the curved surface of the globe
on a flat piece of paper. But any map that is created to do this will
be distorted in some way.

Key to symbols

AERIAL PHOTOGRAPH
A photograph of an area taken from an
aeroplane gives an accurate representation
of what an area looks like. However, this
photograph will not show the conventional
symbols that make a map usable.

In the cylindrical projection, the
imaginary sheet of paper is rolled
around the Earth, touching it at the
Equator. A map designed in this
way always shows the north at the
top, but the areas are distorted.

Peters’ projection

River

Building

Gmund in
Austria

PROJECTIONS

To display the curved surface of the
Earth accurately on a flat sheet of
paper, a technique called projection
is used. Imagine that the Earth is
transparent and that there is a light
at the centre. This light throws
shadows of the Earth’s surface
features on a flat sheet of paper
positioned nearby. The shadow
image that falls on the sheet of
paper is the basis of the map.

MERCATOR

The Mercator projection, first published in 1569, is
based on the cylindrical projection. As directions are
not distorted, it is useful for navigation and
meteorological maps in which wind directions
are important. However, the distortion of
areas is so great that Greenland appears

bigger than Africa,
when in fact it has
only about one-
twelfth of its area.

Flemish geographer
Gerardus Mercator, born
Gerhard Kremer (1512-94)

Mercator’s projection

np:. .i.

EX”

l X

rrt 1

d—

. i

- -!

j 1

Hotel
Church
Land contours

Road

Zenithal projection
PETERS’ MAP

The Peters’ map was designed in
1977 by Arnos Peters. This map
shows the true sizes of continents.
But, for Peters to achieve this, the
shapes of the continents have had
to be stretched.

Conical projection

In the conical projection,
the imaginary paper
forms a cone, touching
the Earth along a
particular line of latitude.
The map drawn in this
way shows the least
distortion to areas.

In the zenithal or
azimuthal projection,
the paper touches the
globe at one point. If
this point is the Pole,
then the lines of
longitude show their
correct anales.

Find out more

Telescopes on Earth p.297
Telescopes in space p.298
Satellites p.300
Space probes p.301
Space stations p.304
Fa c t finder p . 414

240

WEATHER

RAIN

People who have a lot of
rainy weather will know
that a sky full of dark
grey-black clouds
means it’s going to
rain. Rain clouds are
deep and filled with
rain. They stop the
Sun’s rays from shining
through to the ground.
The deeper and darker
the clouds, the more rain
is likely to fall.

The LIVES OF US ALL are affected by the
weather - what we eat and drink, what we wear,
how we behave, and what our homes are like.
Weather has even shaped the landscape. Wind
and rain, snow and ice all wear away the rocks
and grind down the mountains. Weather is with
us all the time. It is the state of the air at any
particular place and time. It can be hot, cold,
windy, still, wet, or dry. In some places it changes
from day to day; in others it stays much the same
all year round. The usual weather of a place from
year to year is called its climate. Climate depends
mainly on how far north or south of the
Equator a place is and therefore how
much sun it gets.

Heavy clouds
over Asia

Clouds and rain
over the tropics

over Antarctica

SUN GOD

Many ancient civilizations
worshipped special gods who they
thought were responsible for the
weather. The Aztecs of Mexico
worshipped the Sun god Tonatuich
to ask for sunshine to ripen their
crops. Without enough sunshine,
the crops failed and there was
famine. Tonatuich and all that he
represented was so important to
the Aztecs that they built temples
and even sacrificed humans in
their eagerness to please him.

Swirl of clouds
in a depression

Clear skies
over the
Sahara
desert

CROP DAMAGE

Strong winds, rain, and
hail are all bad news for
farmers as crops can be
severely damaged by them.
Forecasters try to give
farmers warning of bad
weather so that they can
take precautions. All the
oranges in this pile from
California, in the United
States, have been spoiled
and are unfit for sale.

SUN

The places with the hottest weather in the
world are the dry deserts, a little way away
from the Equator. Here, there are no
clouds to stop the sun getting through.
The Sahara desert in Africa has cloudless
skies nearly every day.

241

WEATHER

Find out more

Changing climates p.246
Winds p.254

Formation of clouds p.262
Rain p.264
Sun p.284
Earth p.287

EDWARD MAUNDER

The British astronomer
Edward Maunder
(1851-1928) was
surprised to find that
historical records of
the Sun’s activity
showed there were no
sunspots at all between
1645 and 1715. This is now
called “the Maunder
Minimum”. At the same time, Europe
was so cold that the period is known as
the “Little Ice Age”. Maunder married
his assistant Annie Russell and worked
closely with her. She was one of the
world’s first women astronomers and
became famous in her own right.

DROUGI IT CYCLE
Some scientists think that sunspots affect the weather. In
some parts of the world, the rains have failed roughly
every 22 years - every two sunspot cycles - causing severe
drought. This happened in North America in the 1930s,
the 1950s, and the 1970s. If this sunspot theory is
correct, the rains are due to fail again at the end of the
1990s. Drought can cause rivers to dry up completely.

Sunshine

SUNSPOTS
Sometimes there are dark spots on
the Sun. They are cooler than the rest
of the Sun, but still as hot as 4,000 °C
(7,000 °F). The number of these
sunspots increases and decreases in
an 11-year cycle. This photograph
was taken on 1 September,
1989, a few months before
maximum sunspot activity.

If THE SUN were surrounded by a shell of ice
1.5 km (about 1 mile) thick, the heat from the
Sun would melt all the ice in just over two
hours. All this heat comes from nuclear
reactions inside the Sun. The surface of the
Sun has a temperature of more than 5,500°C
(9,900°F). The Sun pours out energy in all
directions and our weather and climate depend
on this energy. The Sun is so big that one
million planets the size of the Earth could fit
inside it. It looks so small because it is
150 million km (93 million miles) away. But
even at this distance, the Sun is so bright that
you must never look directly at it: it could
damage your eyes.

The diameter
of the Sun is
108 times
bigger than the
diameter of the
Earth. But the Earth is
a solid ball of rock, and
the Sun is a ball of hot gas.

Making weather

All weather conditions happen
because the heat from the Sun keeps the
air constantly moving. As the surface of the
Earth heats up, it heats the air. Hot air rises
and cooler air moves in to take its place,
stirring up winds. Heat from the Sun makes
water evaporate from the seas and form
clouds. When the clouds cool down, their
moisture falls as rain.

MAGNIFYING THE SUN
The power of the Sun’s rays can be
focused by an ordinary magnifying
glass to burn holes in a piece of
paper. Do not try this without an adult
to help you. In hot, dry countries,
special curved mirrors can be used to
focus the Sun’s rays to heat up a
“hotplate” for cooking.

242

WEATHER

Seasons

1 HE EARTH IS LIKE a spinning top moving in an orbit
around the Sun. The spinning Earth leans over in its orbit,
always tilting the same way. It takes 365.26 days to orbit the Sun
completely. When the Earth is on one side of the Sun, the tilt
leans the Northern Hemisphere towards the Sun. Six months
later, when the Earth is on the other side of the Sun, the
Southern Hemisphere leans towards the Sun. In the

hemisphere leaning towards the Sun, the
Sun rises high in the sky and the days
are long and hot; it is summer. In the
hemisphere leaning away from the
Sun, the Sun rises lower in the sky
and days are short; it is winter.

MIDNIGHT SUN

In regions near the North and South Pole, the
Sun does not set for several months during the
summer. In countries such as Finland it is
daylight for 24 hours. This happens because of
the tilt of the Earth. These areas are called the
land of the midnight Sun. While one Pole has
constant daylight, the other is shrouded in a
dark mid-winter where the Sun never rises.

The Poles have only two seasons: six
months of winter and six
months of summer. _

WHITE
CHRISTMAS
At Christmas, in
December, k is winter in the
Northern Hemisphere. Countries
such as Norway and Canada are
cold and usually have snow. People
have to wear warm clothes when
they go outside.

The Northern
Hemisphere is
tilted away from
the Sun and
has winter. ^

CHRISTMAS ON THE BEACH
In the Southern Hemisphere,
countries such as Australia have
Christmas during the summer. The
weather is just right for a dip in the sea.

Winter in the

Southern

Hemisphere

Find out more

Summer in
the Southern
Hemisphere

Places between the Poles
and the tropics have four
seasons. They gradually
change from spring to
summer to autumn to winter.

At an angle

The Earth leans at an angle of 23.5°
and spins around an imaginary
line joining the North and South
Poles. Depending on the time
^ of year, one hemisphere gets
more sunlight than the other,
and therefore more heat. The
change in temperature
throughout the year causes
the seasons.

The Northern
Hemisphere is
tilted towards
the Sun and
has summer.

•' ‘i

- Places near
the Equator
j i always get the
wJ full heat of the
- Sun.

CASTING SHADOWS

The Sun was worshipped by
some Ancient civilizations.
They knew the Sun’s path
changes. This stone in the
Inca city of Machu Pichu in
Peru is the Intihuatana -
the seat of Inti the Sun
Lord. The Incas noted how
the length of the shadow
the stone cast at noon
changed during the year.

In mid-winter when the
hemisphere is the
furthest it gets from the
Sun, the Pole is in
darkness all day.

Formation of the earth
p.210

Sunshine p.242
Snow p.266
Solar sastem p.283
Polar and tundra lands
p.382

243

WEATHER

Climates

The CLIMATE OF ANY AREA depends on its
position on the Earth’s surface. Land near the
Equator has a hot climate because it gets
sunshine from almost directly
overhead. Far away from the
Equator the climate is always
cold. But climate does not
depend only on how near to
the Equator a place is. Ocean
currents carry warmth around
the world and affect land climate. Distance
from the sea affects the climate of a place, as
does its height above sea level. The higher a
place is, the colder the climate it is likely to
have. Climates are classified into eight main
types, with variations within each one.

MICROCLIMATE

Small areas can have
their own particular
climate, called a
microclimate. Most cities
are covered by a warm
air mass called a “heat
island” that may be 6°C
(11 °F) warmer than
the air outside the city.
This special satellite
picture of Paris, France,
shows the hottest areas
in blue and the coolest
areas in green.

Mountain
climates depend
on the latitude
and height.

O Tundra

Mountain

Places with a warm
temperate climate
have mild wet winters
and hot dry summers.

TEMPERATE

Places with a temperate climate (above) can have rain
any time of year. Their summers are usually not very hot,
and winters are not very cold. But they can suffer short hot
spells in summer and severe snowfall in winter. The prairies
in Wyoming, United States, are in a temperate region.

BY THE SEA

Countries surrounded by sea and with a relatively small landmass
such as Britain or New Zealand have an even-tempered climate:
the winters are mild and the summers are cool. Nowhere is very
far from the sea. These countries have a maritime climate. They
do not experience very great temperature changes because the
sea heats up and cools down more slowly than the land does. It
soaks up heat in summer and releases it in winter.

TROPICAL

Land that has a tropical climate lies in a
band between 10° north and 10° south of
the Equator. It always has hot weather; the
temperature is usually between 24 °C and 27 °C
(75 °F and 81 °F). There are bouts of heavy
rainfall throughout the year with an annual
total of at least 150 cm (59 in) of rain. These
are ideal conditions for rainforests (above).

o Cool temperate
, Warm temperate

Desert

< flli y Monsoon
Tropical

Typical annual
temperature
change in an inner
continental climate

Typical annual
temperature change
in a maritime climate

KEY TO MAP
Polar

244

WEATHER

POLAR

Alaska has a polar climate. The Sun is always low on the
■L horizon, even at midday. A polar climate is very cold and
H dry with strong winds. Summer temperatures only rise
Mig* to about 10°C (50°F) near
H coasts, and it is much
k colder inland.

Places with a
tundra climate
are cold with a
low rainfall and
short summers.

Europe

MONSOON 'W£m
In areas which
have a monsoon
climate, seasons change very
suddenly from wet to dry. In north¬
west India, a dry wind blows
steadily off the land from the
north-east for half the year. Then,
for the other half of the year, a
wind blows from the south-west
bringing torrential rain
\ from the sea.

Africa

Australia

DESERT

New Zealand

Building for the

WEATHER

People build their homes to suit the
climate. In the far north, where it is
always icy, people used to build
temporary homes, called igloos, from

Regions which have a desert climate have less
than 25 cm (9 in) of rain a year. There are no
clouds to block the Sun’s heat by day, or to
hold in the warmth at night. This means the
days are very hot with temperatures up to
52°C (126°F), but nights are very cold. This is
the Pinnacles Desert in Western Australia.

Places with a cool
temperate climate have
rainfall throughout the
year, with warm summers
and cold winters.

slabs of snow and ice. In hot climates,

houses have few inside walls so that air
can circulate. In monsoon areas,
houses are often built on stilts to
avoid flooding. In desert
climates, buildings are
painted white to reflect
the Sun’s heat. In
places with lots of snow
in winter, houses have
steeply sloping roofs so that
the snow can slide off easily.

Igloo from
Alaska,

North America

House on
stilts from
India, Asia

jMgjpa

White-painted
house from
Egypt, Africa

House with a
sloping roof from
Switzerland, Europe

Find out more

Heat transfer p.142
Seasons p.243
Changing climates p.246
Temperature p.251
Deserts p.390
Polar and tundra lands
p.382

Mountains p.384
Fact finder p.4 16

245

WEATHER

Changing climates

Arctic

iurope

North

America

Africa

Indonesia

South

America

Antarctica

iinn

800

900

STUDYING TREE RINGS
Scientists can study the growth
rings in ancient wood to discover
how climates have changed. This
is called dendroclimatology.
Californian bristlecone pine trees
can reveal the climate of up to
9,000 years ago. A wide ring means
that the weather was good for tree
growth that year; a narrow ring
means the weather was too cold or
dry for much growth.

Great ice age

We are living in a period of
warmth between glacial
periods. During glacial periods,
huge ice sheets developed over
North America, north-west Europe,
and Russia. There were probably ice
sheets over Greenland and Antarctica for most
of the time, but varying in size. There may
have been warm periods separating at least 11
glacial periods in a Great Ice Age which
started about 3 million years ago.

The WORLD’S CLIMATES are always changing. In the past, the
world has sometimes been hotter than it is now, and sometimes
cooler than it is now. More than 65 million years ago, when
dinosaurs roamed the planet, there were no polar ice caps and
tropical vegetation grew where it is temperate today. More
recently, in the past million years, there have been times when
great glaciers and ice sheets stretched out from the polar regions.
In the future, there may be a new ice age or a new tropical age.
The climates are changing naturally but they are also being
changed by human activities.

MAXIMUM ICE
The latest ice age was greatest about
18,000 years ago. Ice stretched from
the North Pole as far south as The
Great Lakes in North America
and over most of Britain and
Scandinavia. There were smaller
ice masses in the Southern
Hemisphere.

ICE TODAY
The amount of
ice cover today is
normal to us. It
may seem quite a
small area, but in the
long history of the
Earth it has been rare to
have so much.

LITTLE ICE AGE

The world was noticeably colder than it is now for most of
the past thousand years. There was a period called the Little
Ice Age between about 1550 and 1800. In the worst cold
winters of the 17th and 18th centuries, even the River
Thames in London, England, froze hard. Frost fairs were
held on the river. Even as recently as 1895, the Thames was
partly frozen, as shown by this photograph of Tower Bridge.
Since then, the world has warmed by half a degree Celsius.

JAMES CROLL

British scientist James Croll
(1821-90) was born near Perth in
Scotland. He left school at the age of
13, but continued to study in his own
time. After having many jobs, he was
made keeper of the Andersonian
Museum in Glasgow, Scotland, in 1859.
In 1864, he published a theory that the ice
ages were caused by changes in the tilt of the
Earth’s axis and in its orbit around the Sun. Groll
observed that these changes, which happened in
cycles lasting thousands of years, caused a change in
the balance of seasons. This in turn caused the Earth

to warm or cool.

246

WEATHER

4^ + 2°C (+ 3.6 °F)

INCREASE IN
CARBON DIOXIDE
People burn coal and
oil, and destroy forests
that absorb carbon
dioxide. Because of
this, the amount of
carbon dioxide in the
air has increased by
25 per cent since 1880.

VOLCANIC ERUPTIONS
The eruption of a volcano can be a
reason for a climate change. Dust
is thrown high into the air and
stays in the atmosphere. Mount
Pinatubo in the Philippines
erupted in 1991, throwing huge
clouds of pollution into the air.
These drifted around the world,
blocking out the Sun’s heat, and
the world cooled by half a degree
Celsius for a f ew months.

350

340

330

320

310

300

290

C0 2 (parts per million)

380

370 J (3 Recorded
360 1 Predicted

This graph shows the increase
of carbon dioxide (C0 2 ) in the
air as the number of parts of
C0 2 in 1 million parts of air.

1880 1900 1920 1940 1960

1980 2000 2010

Global warming

Temperature change

+ 1°C
(+1-8°F)

+ 0.5°C
(+ 0.9°F)

Recorded

Top of
range .

Year

JBj

TEMPERATURE CHANGE
Scientists predict a range of
possible temperature
increase due to carbon
dioxide. But there is an
obvious upward
trend.

Bottom of range

1880 1900 1920 1940 1960 1980 2000 2010

EVIDENCE OF PAST CLIMATE
Past climate is revealed by this
ancient cave painting which shows
cattle grazing on the Algerian
plateau in Africa. The cave is now in
the desert. The desertification is due
to natural climate change at the end
of the last Ice Age.

FLOODED LAND
Low-lying regions of the world will
be devastated if global warming
and sea level rise continue. This
computer forecast shows the effect
of a 3-m (10-ft) rise in sea level on
Florida, in the United States. This
could happen within 100 years.

There are natural reasons for the Earth warming up, but people are
contributing to global warming by producing too much carbon
dioxide and other gases, known as greenhouse gases. These gases trap
heat that would otherwise escape into space, strengthening “the
greenhouse effect”. If carbon dioxide and other greenhouse gases
continue to pour into the atmosphere unchecked, the world will
warm rapidly. This computer forecast shows how much temperatures
will increase by 2010, compared with the temperatures in 1950.

-4 cm
(- 1.6 in)

-8 cm
(- 3.1 in)

-12 cm
(- 4.75 in)

1880 1900 1920 1940 1960 1980 2000 2010

Year

CHANGES IN SEA LEVEL

The overall rise in sea level since 1880 corresponds to
the rise in temperature. It exactly matches the amount
by which the upper layer of the ocean would be
expected to expand if warmed by half a degree Celsius.

Florida

coastline today

Sea level rise
of 3 m (10 ft)

Sea level change Year

+16 cm
(+6.3 in)

+12cm
(+4.72 in)

+8 cm
(+ 3.1 in)

+4 cm
(+ 1.6 in)

( ) Recorded

Predicted

This graph shows the
changes in sea level,
compared with the average
for the 1970s.

- Find out more -

Formation of the f.arth p.210
Volcanoes p.216
Ice and glaciers p.228
Growth and development
p.362

Cycles in the biosphere p.372

247

WEATHER

Atmosphere

LlFE ON EARTH EXISTS only because of the atmosphere. It is like a
blanket around the Earth, protecting it from the Sun and providing
the necessary conditions in which animals and plants can live. Other
planets have atmospheres, but these are very different. On Venus, the
air is thick. It contains many more gas molecules than Earth’s
atmosphere and the pressure is 100 times greater than on Earth. The
Sun’s heat is trapped and temperatures reach 480°C (900°F). It is too
hot for liquid water to exist. The atmosphere on Mars is thin. The
Sun’s heat bounces away and temperatures can fall to -120°C (-180°F).
Liquid water cannot exist here either. Conditions on Earth are in
between those on Mars and Venus. Earth is sometimes called the
Goldilocks planet because the conditions
are like Baby Bear’s porridge - just right!

Layers of the atmosphere

The atmosphere is made up of five main
layers: the troposphere, stratosphere,
mesosphere, thermosphere, and exosphere.
The air gets thinner as you go higher,
which is why climbers usually take
oxygen with them when climbing high
mountains. The troposphere is the
only layer in which living things can
breathe normally.

Exosphere

BELT ROUND THE EARTH
This photograph, taken from
space as the Sun sets, shows
bands of air of different heights
(and different densities). The
photo reveals how narrow the
belt of atmosphere around the
Earth is.

Thermosphere

Mesosphere

Ozone

The

with

EARTH FROM SPACE
Satellites can take photos of the
Earth at three different wave¬
lengths at the same time. Infrared
pictures show temperature
changes - black, blue, green, red,
and white showing hot to cold.
Normal photos show the land
and sea. Other pictures show how
much water vapour is in the air.

EXOSPHERE
The top layer of
the atmosphere sits
about 900 km
(560 miles) above Earth.
The air is very thin and gas
molecules are constantly
“exiting” into space. This is why
it is called the exosphere.

THERMOSPHERE
The top of the thermosphere is
about 450 km (280 miles) above the
Earth. It is the hottest layer, as the few air
molecules absorb radiation coming from
the Sun. Temperatures reach as high as
2,000°C (3,632°F) at the top.

MESOSPHERE

top of the mesosphere is about 80 km
(50 miles) above the ground. It is very cold here,
temperatures less than -100°C (-148°F). The
part is warmer because it picks up heat from the
stratosphere just below.

STRATOSPHERE
Up to about 50 km (31 miles)
above the ground lies the
stratosphere. The temperature in
this layer warms from about-60°C
(-76°F) at the bottom to just above
freezing at the top. The stratosphere
contains ozone, a gas that absorbs harmful
ultraviolet rays from the Sun. Today, pollution
is making holes in the ozone layer.

TROPOSPHERE
Weather conditions happen in the bottom
layer of the atmosphere, called the troposphere.
This layer stretches up 20 km (12 miles) from
the ground at the Equator, and about 10 km
(6 miles) at the Poles.

1,000 km

(620 miles)

1,000 km
(620 miles)

/ HOW FAR UP?

/ The atmosphere above

your head stretches up about
1,000 km (620 miles). It sounds
a lot but compare it with distances
on the surface of the Earth. If you
could drive a car straight up at 50
km/h (31 mph), you would be in
space in less than a day! You could
even walk 15 km (9 miles) to the top
of the troposphere in a few hours.

248

WEATHER

Weather iayer

The lowest layer of the
atmosphere, the troposphere, is
sometimes called the weather
layer. It is the layer in which
convection happens - warm air
rises and cold air sinks to take its
place. Clouds form in this layer
too, bringing rain and snow. The
clouds are trapped in the
troposphere because the next
layer up, the stratosphere, is
warmer and acts like a lid. The
troposphere cools from an
average of 15°C (59°F)at the
Earth’s surface to -60°C (-76°F) at
the tropopause (the top of the
troposphere).

^ JAMES GLAISHER

m mm: * A balloonist, Englishman
jiyJames Glaisher (1809-1903),
was also interested in the

discovered that

the air got cooler the higher they jaHsT'*
went. On one flight, Glaisher
fainted because he had no oxygen fe*
equipment or protective clothes. In
1848, Glaisher started the first
newspaper weather report in Europe
for the London Daily News. He also made
some of the first daily charts.

Storm clouds can
reach up to 15,000 m
(49,000 ft) high

Air has to rise to go
over mountains. The
weather on each side
can be very different.

Cirrus clouds are the highest
clouds. They for mat the top
of the troposphere.

Ozone layer

Flying though the
troposphere can be
bumpy because of
the moving air.

Small, puffy, white
clouds form when
bubbles of warm air
rise and cool.

Troposphere

The air is full of water vapour,
which turns to water droplets in
some clouds and falls as rain.

Lightning is caused by
the build-up of static
electricity in storm clouds.

Almost all clouds form in the
bottom 10-12 km (6-7 miles)
of the atmosphere.

Find out more

ATMOSPHERIC POLLUTION

The rays of sunshine shining through this window in St Peter’s
Cathedral in Rome, Italy, show that the air is full of particles of
dust and dirt which you cannot see most of the time. Try
hanging a clean, white handkerchief outside your window on a
dry, calm, cloudy day and look at it several hours later. You may
find that your handkerchief has got dirtier just by being outside,
especially if you live in a city. Smoke from factories and fumes
from cars pollute the atmosphere. Some pollutants get trapped
just above the ground and this causes people to have breathing
problems and eye irritations.

Chemistry of air p.74
Heat transfer p.142
Clouds p.260

Formation of clouds p.262
Forecasting p.270
Mercury and venus p.286
Mars p.289

Cycles in the biosphere p.372
People and planet p.374

249

WEATHER

Air pressure

80 cm
(31.5 in)

75 cm
(29.53 in)

70 cm
(27.56 in)|

65 cm
(25.6 in)

60 cm
(23.62 in)

55 cm
(21.65 in)

50 cm
(19.69 in)|

45 cm
(17.72 in)

40 cm
(15.75 in)

35 cm
(13.78 in)

30 cm
(11.8 in)

25 cm
(9.84 in)

We CANNOT SEE AIR, but it is all around us. Gravity
pulls the atmosphere down on to the Earth. This is air
pressure. You do not normally feel this pressure
because there is an equal pressure inside your body
pushing outwards. At ground level, the pressure is
greatest because there is a large weight of air overhead
pushing down. The higher you go, the less air there is
so the less pressure it exerts. You have to boil an egg for
longer to cook it at high altitudes because the lower air
pressure allows water to boil at a lower temperature.
Aeroplanes flying high in the sky have pressurized \ \

cabins so that there is enough air to breathe. \\ \ '

High and low pressure

Pressure is not the same everywhere. If the air is
cold, it sinks, pushing down to create a higher pressure
on Earth. As the air is squashed together, it warms up
and so brings fine weather. If the air is warm, it rises
and so there is a lower pressure on Earth. The
warm air may also evaporate water from the sea
and take it up to form clouds. This is why
low pressure can
bring rain.

MAPPING PRESSURE
Pressure is measured in
millibars (mb). On
weather maps, all the
areas of equal pressure
are joined to make a
curving line called an
isobar. Areas of high
and low pressure can
then be easily identified.

In a high
(an area of
high pressure),
air sinks to the
ground and
spreads. It absorbs
moisture and usually
brings fine weather.

BAROMETERS

In a low (an
area of low
pressure), air
rises and
condenses
into cloud.

20 cm

(7.87 in)

1 cm (0.39 in)
13.33 millibars

Air presses
down on the
mercury and
forces it up
the tube.

Mercury is

In La Paz, at 3,658 m
(12,000 ft) high, the
standard pressure is
690 mb.

Pressure is

shown in millibars and

pounds per square inch.

In Concepcion at
490 m (1,600 ft)
high, the
standard

pressure is
1,013 mb.

Air pressure is measured with
barometers. An aneroid
barometer looks a bit like a
clock. It contains a sealed
metal box with no air
inside. The pointer is
joined to the box.
When air pressure
rises, the box is
squashed inwards
and the pointer shows
the change on a dial.
Changing air pressure is
a good indicator of
weather to come.

CHANGING PRESSURE
A glass tube standing in an open
dish of mercury is a simple way of
seeing how air pressure changes. As
air pressure rises and falls, the level
of mercury in the tube changes.

PRESSURE AND
ALTITUDE
As you go up a mountain,
the air pressure gets lower
and lower. This is shown
by the standard pressure
of two cities in the
Andes mountains in
Bolivia - Concepcion
and La Paz.

Find out more

Gravity p.122
Pressure p.127
Atmosphere p.248
Fronts p.253

Formation of clouds p.262
Forecasting p.270

250

WEATHER

Temperature

Always cold - below 0 °C (32 °F) ( ^

Mild summer, cool winter

The liquid in
each tube moves
an indicator
which stays at
the highest or
the lowest
temperature
reached.

Heat from the sun

Temperature is different around the world
because of the way the Sun’s rays strike the
surface. At the Equator, the Sun’s rays hit the
Earth straight on and so these areas are usually
hot. At the Poles, the Sun’s rays hit the Earth at
a shallow angle so their heat is spread out.

The Sun’s rays meet the Poles at an angle because the Earth
curves away.

Always hot - above 20 °C (68 °F)
(/""^Always mild - between 10-20 °C (50-68 °F)

TEMPERATURE VARIATIONS
The temperature varies over the
24 hours of the day. It is colder at
night and warmer in the daytime.
In areas midway between the
Equator and the Poles, the diurnal
(daily) variation in temperature
may be about 10 °C (18 °F).

Hot summer, cool winter

> Hot summer, cold winter

/ \Cool - 0-10 °C (32-50 °F) - summer,
cold winter

HIGHEST TEMPERATURE
The highest temperature ever recorded
was taken at al’Aziziyah, close to the
Sahara Desert in Libya. It was 58 °C
(136 °E) in the shade.

Depending ON WHERE YOU ARE, the Earth may be hot or cold.
The average temperature at Dallol, Ethiopia, is 34 °C (93 °F). The
average temperature at the Plateau research station, Antarctica, is
-56 °C (-70 °F). Temperatures are always highest near the Equator
and where there is no cloud so that heat from the Sun can easily
reach .the ground. They are lowest far from the Equator and where
there is no cloud, so that heat can escape easily into space. The
temperature also depends on how shiny the Earth’s surface is - this
is called its albedo. Areas of snow and ice have a high albedo so they
reflect solar radiation back into space: temperatures remain low.

Bare soil and forests absorb more radiation and keep warm.

Hot summer, mild winter

The Sun’s rays meet the Equator straight on

THERMOMETERS

Temperature should
always be measured in the
shade. The temperature
change in a day can be
measured with a
maximum and minimum
thermometer. This
thermometer shows the
highest and lowest
temperature of the day.

In La Paz, at
3,658 m (12,000
ft) high, the
temperature in
June is 17 °C
(62 °F).

In Conception at 490 m
(1,600 ft) high, the
temperature in June is
27 °C (80 °F).

COLDEST PIACE
The coldest temperature ever recorded
was taken at Vostock Station, Antarctica,
in July 1983. It was -89 °C (-129 °F) -
colder than a freezer at home.

AIR TEMPERATURES
The ground is warmed up by
sunlight falling on it. But the
air is warmed by heat rising
from the ground. This is why
it is always colder at the top
of a mountain than at the
bottom, as shown by the
average maximumjune
temperatures in La Paz and
Conception in Bolivia.

Find out more

Heat transfer p.142
Seasons p.243
Climates p.244
Weather watching p.272
Polar and tundra lands p.382
Deserts p.390
Fact finder? A\C

251

WEATHER

Humidity

FERDINAND II

Ferdinando de
Medici, Duke
of Tuscany,
(1610-70) was
an Italian
experimenter
who worked
with Galileo. In
1655, he
invented a
condensation
hygrometer. This instrument
calculated the humidity of the air
by measuring the amount of dew
that appeared on a cool surface.

He also invented the modern
thermometer. A specially sealed
glass tube made sure the results
were not confused by the effect
of air pressure.

ADAPTING TO HUMIDITY
Hard physical work in humid air is
exhausting if you are not used to it
because your body finds it hard to
keep cool. But with practice, the
body gets more efficient. The
British athlete Yvonne Murray
trained in a greenhouse to become
used to high humidity. She was
going to compete in the World
Championships in Tokyo, Japan,
where it would be much more
humid than in Britain.

A model of a
man and a
woman stand
on the
turntable. In
humid
conditions,
the stretched

hair allows
the turntable to turn, and the man
appears. In dry conditions, the
hair shrinks, pulling the turntable
so that the woman appears.

Measuring humidity

The amount of water vapour in the air can be
measured with a hygrometer. This measures
absorption or condensation of water from the
air. There are different kinds of hygrometer.
The earliest one was a sponge. When the air
was humid, the sponge absorbed water and
became heavier. A weather house is a simple
hygrometer that indicates wet weather by the
stretching of a hair.

Farming is difficult in deserts such
as this one in Saudi Arabia. There
is very little water for people,
livestock, or crops.

EFFECTS OF HUMIDITY
Water vapour in the air is important
for life to survive. Deserts occur where
humidity is low - less than 10 per cent.
If the normal rains fail to fall in an
area, the people may starve. At the
opposite extreme where humidity is
high, jungles grow.

Farming is successful
in areas of medium
humidity, such as
Britain.

Where humidity is very
high, rainfall is heavy. This
creates ideal conditions for
plants. This rainforest is on the
island of Grenada.

inside the house stretches
when it is wet and shrinks
when it is dry. As it
stretches and shrinks, it
turns a turntable.

When THE AIR CONTAINS lots of water vapour, the
weather is described as humid. The warmer the air is, the
more moisture it can hold. If the air cannot carry any
more water vapour, the humidity is 100 per cent.

At this point the vapour condenses back into
water and forms clouds, fog, or rain. Plants grow
well in high humidity but it is uncomfortable for
us. It is difficult for the body to cool down
because sweat cannot evaporate into the air. Low
humidity is better for us but it is hard
to grow crops. Scientists often talk
about relative humidity. This is the
amount of water vapour in the
air relative (compared) to
the maximum it can
hold at that
temperature.

The woman is
outside the house
when the humidity
is low.

Find out more

Changes of state p.20
Heat p.140

Formation of clouds p.262
Fog, mist, and smog p.263
Rain p.264

Weather watching p.272
Deserts p.390

Tropical rainforests p.394

252

WEATHER

Fronts

WEATHER
MAP
Fronts are
shown on a

weather map by spiked and bumpy
lines. Spikes indicate a cold front; bumps
indicate a warm front. As a depression
travels, the cold front often catches up the warm front.
Then spikes and bumps alternate along the line. This is
called an occluded front.

AIR MASSES

There are four main air masses
that form over different parts of
the Earth. These air masses affect
the weather of the area over
which they lie. They are blown by
the winds and, where they meet
and compete, the weather can be
very changeable.

UNDER A COLD FRONT
A cold front brings clouds and
rain immediately. There may
be strong gusts of wind, called
squalls, or violent storms.

COLD FRONTS

A cold front has cold air behind it. The front is
much steeper than a warm front. The cold air
pushes underneath the warm air, and water
vapour rises and condenses into cloud and rain.
The air pressure drops and the wind gets
stronger. As the front moves on, there are often
showers from rain clouds trailing behind.

k Warm moist
Tropical maritime

Cold wet Polar
maritime

UNDER A WARM FRONT
When a warm front arrives, at first
there is no change in the weather.
The first sign is wispy clouds high
in the sky, then some light drizzle.

___ Wispy

clouds

Warm front

The world’s weather is carried around the

Earth by huge swirling weather systems called highs
and lows - areas of high and low pressure. Areas of
high pressure, called anticyclones, are made by
falling air. They move slowly causing the weather to
be settled. The air is dry, bringing hot, dry weather
in summer and cold, clear weather in winter. Areas
of low pressure are called cyclones (depressions).
They are caused by rising air. The air is moist,
bringing cloud, rain, or maybe snow. A depression
is formed where a belt of warm and cool air collide.
The two do not mix, but push into each other. Fronts
form at the boundaries of the air masses and the
weather becomes unsettled. A depression can be
hundreds of kilometres across but usually
air passes overhead in less than 24

hours. A warm front is usually the
first to arrive.When it has
passed, a cold front
follows close behind.

Cold air

WARM
FRONTS

A warm front has warm, moist air behind it. This warm
air rises up over the cold air and forms cloud along the
front. When the warm front has passed, there will be dry
weather before the cold front arrives.

This depression is
travelling from
right to left.

Warm

Rain falls

behind Heav Y rain

the front alon 9 the

Occluded

Cold front

Cold air

Warm front

Cold front

, Hot dry Tropical
continental

/* x Cold dry Polar
continental

Find out more

Form

Climates p.244
\IR PRESSURE P.250
Humidity p.252
Clouds p.260

ATION OF CLOUDS

Forecasting p.270

p.262

253

WEATHER

DOLDRUMS

Along the Equator there is
an area of low pressure
where the trade winds
meet. In this area, called
the doldrums, there is very
little wind. When ships
were powered only by sail
they sometimes got stuck
in the doldrums. Food and
water began to run out and
all they could do was wait
until they drifted towards
the trade winds.

WIND DIRECTION
Windsocks are used at small airports
to show pilots the strength and
direction of the wind. A floppy
windsock means that the wind is
only light. When strong winds blow,
the sock is filled with moving air
and billows in the direction the
wind is blowing. A wind is described
by the direction from which it is
coming. For example, a west wind
comes from the west; a north wind
comes from the north.

Winds are turned to the
right in the Northern
Hemisphere.

The AIR NEVER STOPS MOVING. As it moves, it carries heat
and water around the globe, giving us our weather. World winds
blow because there is a difference in air pressure and temperature
between one place and another. Winds blow from an area of high
pressure to an area of low pressure. You can show this with a
balloon. When you blow up a balloon you squeeze in more and
more air until the balloon is under high pressure. If you let the air
escape, it rushes out like a wind to where the pressure is lower.
When air is warm, it is less dense than cold air and rises up into
the sky causing an area of low pressure. Cold air sinks down to the

Earth and moves in to fill the gap left by
the warm air. It is this circulation
of air that forms the winds.

Doldrums

Polar Easterlies

Westerlies

JET STREAMS

At about 10 km (6 miles) above the
ground, strong winds called the jet
streams circle the Earth - one in
each hemisphere. This photograph
from space shows jet stream clouds
over Egypt. The jet streams are only
a few hundred kilometres wide but
sometimes stretch halfway round
the Earth. They usually blow at
about 200 km/h (125 mph),but
can go twice as fast. The jet streams
play a large part in moving the
major air masses and therefore
affect the weather considerably.

LOCAL WINDS

All over the world there are regular local
winds that have their own names. For
example, the Fohn is a dry wind that
blows from the Alps in Europe. This
storm is blowing up over the
Matterhorn in the Alps. Other local
winds include the Chinook, a dry
wind which blows down the east of
the Rockies in North America. It
creates rapid changes in temperature
and humidity. The Doctor is a
refreshing sea breeze that develops
around midday in Fremantle, Australia.
The Pampero is a cold, south-westerly wind
blowing from the Andes in South America.

Winds

Trade winds blow from the
north-east and the south-east,
either side of the Equator.

Warm air rises and
spreads out.

Cold Polar

Warm air
rises over
Polar air.

Winds
are turned
to the left in
the Southern
Hemisphere.

Westerlies

Polar Easterlies are
caused by cold Polar air
sinking and spreading out
to warmer areas.

Main winds

Winds which blow
all the time in the
same area of the world
are called prevailing
winds. They determine the
weather patterns around the
globe. They move because the
Equator gets more heat from the Sun
than the Poles. Hot air moves north
and south from the Equator, where it
cools. The direction of the winds is
also affected by the Earth’s spin.

Cool air sinks and
rushes in to replace
the warm air.

254

WEATHER

Warm air

Sea breeze

Land

Sea

Sea breezes

Land and sea breezes happen only in hot, sunny
weather. They are convection currents caused by
the land and the sea heating up and cooling down
at different rates. During the day, the land
heats up more quickly than the sea. Warm
air rises from the land and forms an area
of low pressure. Air moves in from the sea
to replace this rising air, causing a sea
breeze. If there are no hills to act as a wind
break, the breeze can blow up to 30 km
(18 miles) inland.

Cold air

Sea

Land breezes

At night, the land cools down more quickly
than the sea. Cold air sinks over the land
and pushes out to sea. The air over the sea
is still warm so it rises. The colder air moves
in to replace it causing a land breeze.

WIND POWER
The wind can be captured to
create electricity. In an
experimental station in the United
States, rows and rows of windmills
are driven naturally by the forceful
local winds. The windmills drive
turbines which are connected
to an electricity generator. They
can collect enough energy to
light and heat a small town.

Unlike coal and nuclear power
stations, wind turbines do not
create any pollution.

Find out more

Energy sources p.134
Heat transfer p.142
Seasons p.243
Air pressure p.250
Temperature p.251
Fronts p.253

Land

WIND RECORD
The windiest place in the world
is George V Coast in Antarctica
- shown here. The winds
regularly blow at 320 km/h
(199 mph). The strongest wind
ever recorded on the surface of
the Earth was 371 km/h
(231 mph) at Mount
Washington, in New Hampshire,
United States, on 12 April 1934.

Land breeze

TOWER OF WINDS

In the 1st century B.C. the Greek
astronomer Andronicus built a
Tower of Winds called a
horologium. It had eight sides and
on each one was carved a wind
god. Each god showed off the style
of his own wind. The god of the
cold north wind was Boreus who
was carved as an old man wearing
warm clothes and playing a conch
shell. The god of the warm east
wind was in light clothes carrying fruit and grain.

255

WEATHER

Wind strength

FRIEND AND FOE, the wind has a large effect
on our lives. Sometimes it blows gently giving a
refreshing breeze. At other times it blows strongly,
creating storms, gales, and hurricanes in which
widespread damage is caused and people are killed.
The first attempt to standardize the reporting of
winds was made by Admiral Sir Francis Beaufort in
1805. He devised a scale to help sailors estimate
wind strength. In the past, the energy of the wind
was used to drive windmills to grind corn. And
even now, with all our modern technology, the
wind’s energy is still used. But now it drives
wind turbines to generate electricity.

0. Calm. Chimney smoke
rises straight up.

1. Light air - average
wind speed 3 km/h
(1.8 mph). Smoke
drifts gently.

2. Light breeze - wind
speed 9 km/h
(5.6 mph). Leaves
rustle. Wind felt
on your face.

3. Gentle breeze - wind—
speed 15 km/h (9.3 mph).
Leaves and twigs on trees
move. Flags flutter.

19th-century

anemometer

4. Moderate wind - wind speed 25 km/h
(16 mph). Small branches move. Paper
blows around.

ANEMOMETER
An anemometer

is an instrument r\ II ^

for measuring

wind speed. The first

anemometers had a ball J

that was blown up a

curved scale. Anemometers today have

three or more cups mounted on the end

of arms that spin round a vertical pole.

As the cups catch the wind, the arms

spin round, and the speed is recorded.

5. Fresh wind - wind speed
35 km/h (22 mph). Small
trees start to sway.

6. Strong wind- .
wind speed
45 km/h (28 mph).

Difficult to control umbrella.
Large branches move.

7. Near gale- wind speed

56 km/h (35 mph). Whole trees sway.

Beaufort scale

This scale of wind strength was originally based on
the effect that wind speed had on a full-rigged sailing
ship and stated the amount of sail the ship should
carry at different levels of wind. The scale is still in
use today and has been adapted for use on land.
There are 13 levels of wind strength on the scale,
ranging from dead calm to hurricane.

8. Gale - wind speed 68 km/h
(42 mph). Difficult to walk into
wind. Twigs broken off trees.

9. Severe gale - wind speed
81 km/h (50 mph). Small branches,
slates, and chimneypots blown off.

10. Storm - wind speed

94 km/h (58 mph). Houses damaged.

Trees blown down.

11. Severe storm - wind speed
110 km/h (68 mph). Serious damage.

SIR FRANCIS
BEAUFORT

\ Born in Ireland, Sir
Francis Beaufort
(1774-1857) was
only 12 years old
when he joined the
British Royal Navy as
a midshipman. He
WF devised his wind scale
after many years of
observation of ships at sea.

12. Hurricane - wind speed more than
118 km/h (73 mph). Widespread damage.

KITE FESTIVAL
The Chinese flew kites
2,500 years ago. Today,
people all over the
world fly kites for fun.
Injapan, traditional
kites are decorated
with legendary
characters or animals
that symbolize
different things.

Find out more

Er*

■JERGY SOURCES P.L
Winds p.254
Hurricanes p.258
Tornadoes p.259

256

WEATHER

Thunder and lightning

DARK THUNDERCLOUDS form on hot, humid days. A storm cloud
is usually about 5 km (3 miles) across and 8 km (5 miles) high. Often,
an individual thunderstorm is just one “cell” in a group of storms
that may be 30 km (19 miles) across, and can last for five hours or
more. Sometimes a single cell can become a “superstorm”, more
than 50 km (31 miles) across. This can produce large hailstones as
well as thunder and lightning. If the storm is overhead, you can hear
thunder at the same time as you see lightning. If it is not overhead,
you can see the lightning first because light travels much faster than
sound. If you count the seconds between the lightning and the
thunder and divide by three, that gives you a rough idea of how far
away the storm is in kilometres; for miles, divide by five.

SHEET
LIGHTNING

When a flash of lightning lights up the
sky, it is sheet lightning. This is a stroke
of lightning that occurs within the storm
cloud and doesn’t come down to Earth.

Thunderstorm

Thunderclouds form
when warm, wet air
surges upwards into
the sky and cools
dramatically.

Inside these
clouds, some of
the water
freezes and

strong air
currents make
the ice and
water droplets
bump together.

This knocks tiny
charged particles
called electrons from
the ice and so there is a
build-up of electrical charge.

This charge is released by a stroke
of lightning. The lightning heats the air around it
to an incredible 30,000 °C (54,000°F) - five times
hotter than the surface of the Sun. This heat
causes the air to expand very fast - in fact faster
than the speed of sound. It is this which causes
the crash of thunder.

ELECTRICAL
CHARGES
Inside a storm
cloud, the
bumping of
water and
ice particles
creates a build
up of static

electricity. Positive charge piles up at the top of
the cloud; negative charge piles up at the
bottom and tries to escape to the ground. When
the difference between the charges is large
enough, a lightning stroke flashes either from
the bottom to the top of a cloud or from the
bottom of the cloud to the ground.

FORKED LIGHTNING
Forked lightning begins when a
“leader stroke” zigzags towards
the ground at 100 km/second
(62 mps), taking the easiest path.

It creates a path of electrically
charged air for a return, or main,
stroke to shoot back immediately. It is
this return stroke that we see.

GOD OF THUNDER

Thor was the Norse
god of thunder,
depicted here in a 10th-
century bronze from
Iceland. He was said to
be a huge man with
red hair and beard.
He was a symbol of
tremendous strength
and power and was
believed to make
thunderbolts which
fell from the clouds.

SAFE PI.AGE

If you are caught out in a storm, avoid sheltering under an
isolated tall tree. Lightning looks for the quickest path to
the ground and could strike the tree. One of the safest
places to be is inside a car. If the car is struck by
lightning, the steel frame conducts the electricity over
the surface of the car to the ground.

Find out more

Sta

CURI

lTIC electricity p.

LENT ELECTRICITY 1

Sound p. 178
Light p.190
Hail p.267
Sun p.284

146

p.148

257

WEATHER

Hurricanes

HURRICANE ANDREW

In 1992, hurricane Andrew swept across Florida,
in the United States. A warning was issued and
many people evacuated the area. The hurricane
killed 15 people, and made 50,000 homeless.

Sometimes called tropical cyclones, typhoons, or

willy-willies, hurricanes can rip up trees, destroy crops, and flatten
buildings. Torrential rain causes flooding and coastal regions may
be swamped by huge waves whipped up by winds that blow as fast
as 300 km/h (185 mph). Hurricanes start to form when the Sun’s
heat stirs up moist air over the oceans, where the temperature is
more than 27°C (80°F). At first, the ring of low pressure at the
centre of the storm, called the eye, can be more than 300 km
(185 miles) across and the winds only gale force. But as the eye
narrows to about 50 km (30 miles) across, the winds begin to swirl
around it at hurricane force.

1. At the
beginning of a
hurricane, air is
sucked in towards
the centre of the
area of low
pressure, creating
fierce surface
winds.

Air spirals
anticlockwise in
storms in the
Northern
Hemisphere, and
clockwise in the
Southern

What happens in a hurricane?

At the eye in the centre of a hurricane, it is calm. A
huge column of rising hot, moist air develops around
the eye. As this humid air spirals up and cools, the
water in it condenses into rain. Although the heaviest
rain and strongest winds occur right next to the eye of
the hurricane, lesser effects can be felt up to 400 km
(240 miles) away.

2. If the eye of the
storm is very wide,
the surrounding
winds will be
weak. As the eye
becomes
narrower, the
wind speed
increases
violently.

STORM OR HURRICANE?
Meteorologists are always on the
look out for possible hurricanes.
Satellites are used to take
pictures of developing
hurricanes. The satellite images
help meteorologists to detect
where a storm is likely to
develop into a hurricane and to
predict its likely path.

4. At full strength, the
winds spin round at
over 118 km/h
(74 mph). The
hurricane only runs out
of steam when it
passes over land or
over cooler water -
below 27 °C (80°F).

A huge circle of
clouds is
formed by air
spreading out
from the top
of the
storm

Scientists are trying to make a second eye in a hurricane by
“seeding” it with salt, ice, or silver iodine crystals. If this eye
eye, wind speed could be
reduced.

CLEMENT WRAGGE

Australian Clement
Wragge (1852-1922)
introduced the idea
of naming hurricanes.

He decided to give
them women’s names.
It is said he used the
names of people he
disliked! Since 1970, an alphabetical
list of alternating male and female
names has been drawn up every year.
Each time a hurricane is detected, it
is given the next name on the list.

3. As the
hurricane
progresses, the
air moves even
faster and swirls
upwards in an
enormous spiral.

Find out more

For]'

Air pressure p.25
Humidity p.252
^IND STRENGTH P.2
NATION OF CLOUDS
Rain p.264
Forecasting p.27

!56

> p.262

258

WEATHER

Tornadoes

The HIGHEST WINDSPEEDS on Earth occur

SEA MONSTERS

If a tornado forms over sea, it is known as
a waterspout. When it touches the surface
of the ocean, water is sucked up inside
the spinning wind. Waterspouts seem to
rise up out of the sea like enormous dark
grey serpents. They are probably the basis
of legends about sea monsters.

Spiral forms in the water
of the upper bottle.

TORNADO IN A BOTTLE
To see how a tornado works,
take two plastic bottles with
screw tops and glue the tops
together. Make a small hole
through both tops with a nail.
Fill one bottle about three-
quarters full with water, and
screw the double top on.
Screw the empty bottle on to
the top of the full bottle.

Turn the two bottles upside-
down, and give the water a
slight swirl to set it off. It will
form a spiral in the middle,
just like a tornado.

in tornadoes. Winds whip round in a twisting
funnel of air at maybe 500 km/h (310 mph), far
higher than the windspeed inside a hurricane,
although we cannot know exactly as
meteorological instruments do not survive in the
strongest tornadoes. Tornadoes are small,
extremely powerful whirlwinds that form very
suddenly and often occur in groups. They are
most common and most violent in the United
States, where more than 500 spring up every
year. A tornado may measure anything from just
a few metres to more than 100 metres (330 ft)
across and can travel for more than 200 km
(125 miles). As it goes, it can suck up anything in
its path, including buildings, trees, and trains,
and then drop them when its force fades.

Tornado formation

Tornadoes form when a long

funnel of quickly rising warm

air stretches up from the

ground, often to a

thundercloud. They may

happen when the ground gets

very hot and a bubble of air starts rising.

In North America, they form when cold, dry air
from the Rocky Mountains flows east on top of warm,
wet air moving north from the Gulf of Mexico. If
the updraught of air is set spinning by strong winds, the
updraught can become a tornado.

Bf Pressure in
the centre of
the tornado is
hundreds of
millibars lower than
normal atmosphere.
Buildings can explode
as air inside bursts out
towards the area of
low pressure.

STRANGE RAIN
As a tornado loses energy and
disintegrates, things that it has
picked up come crashing down.
This could be the cause of strange
“rain”, such as frogs, falling. When
a tornado passes over water, it can
suck up small fish and frogs as well
as the water. These can be carried
a long way before being dropped.

Whirling funnel of
air stretches to the
ground like a huge
vacuum cleaner.

TORRO SCALE

Tornadoes develop so suddenly that it is
impossible to forecast the exact time and
location of a tornado strike. When weather
conditions that encourage tornadoes develop,
general warnings are broadcast and then
updated with more specific alerts as storms are
identified. The Torro tornado intensity scale
classifies the speed and destructive power of a
moving tornado on a scale from 0 to 12. For
example, Torro force 1 is described as mild:
small trees will be uprooted and chimney pots
removed. Torro force 12 is described as a
super tornado: even steel-reinforced buildings
will be seriously damaged.

Find out more

\IR PRESSURE P.25C
IND STRENGTH P.2'
Hurricanes p.258
Clouds p.260
Rain p.264

)

259

WEATHER

Clouds

WEATHER WITH CIRRUS
Cirrus clouds are often
the first sign of fine
weather coming to
an end. The Sun
| and Moon can look
I as if they are
| surrounded by a
halo when they
shine through a layer
of cirrus clouds. This
is a strong indication
that rain is on the way.

Cumulus

Cumulus are puffy, white clouds with a
flat base. They look a bit like pieces
of cotton wool drifting about in
the sky. They are sometimes
called cauliflower clouds
because of their shape.

Cumulus clouds are
produced by rising
bubbles of warm air
called thermals.

Cirrus

Cirrus clouds form high up in the sky - so
high, that the water inside them is frozen
to crystals of ice. Sometimes, cirrus clouds
create a complete layer of white cloud.

CLOUDS ARE RESPONSIBLE for many aspects
of weather. They therefore give some of the best
clues as to what the weather will be like in the
next few hours or days. If you look up and see a
sky full of dark, menacing clouds, you know that
it is likely to rain heavily. Fluffy, white clouds
form on a warm sunny day and mean the
weather will probably stay warm and dry. There
are three basic types of cloud: cumulus, meaning
heaped, stratus, meaning layered, and cirrus,

meaning feathery. All the other many shapes
and shades of cloud are a mixture or
variation of these three.

WEATHER WITH
CUMULUS

Small, puffy, cumulus
||§§, clouds are of ten seen
on hot summer
days. They
disappear at
night when
the air is no
longer heated by
the ground, and
warm air does not rise
to form them.

LUKE HOWARD

In 1803, Luke Howard (1772-1864)
devised a scheme for the classification
of cloud types. He was a pharmacist
and a keen amateur meteorologist. He
tried, but failed, to find a link between
the Moon’s phases and the weather.

Howard used Latin names to identify each
type of cloud, as Latin names were being
used in the classification systems for animals and
plants. Howard’s classification is based upon the shape
of clouds and their height above the ground.

Stratus

Stratus clouds form in layers that build up
and can reach across the whole sky. In
hilly regions, a layer of stratus cloud often
covers the ground as a wet mist.

WEATHER WITH
STRATUS
Stratus clouds
form perhaps
the most
depressing
types of cloud.
They bring
persistent
drizzling rain or
light falls of snow.

260

WEATHER

Cirrocumulus
are a heaped-
up form of cirrus.
They are clouds of
icy particles which
often make a pattern
like fish scales,
called a
mackerel sky.

They bring

unsettled

weather.

Cirrostratus is a
layer of cirrus
clouds. They
look like a
transparent, white
veil high in the sky
and often mean
that wet weather
is on the way.

Altostratus clouds form a thin, ""T
watery sheet of cloud across
the sky. It is thin enough for the
Sun to shine weakly through.
Altostratus often indicate
that rain is on its way.

Altocumulus clouds are a mixture of ice and -
super-cooled water. They are flattened globules of
white and grey cloud and sometimes signal a
thunderstorm at the end of a long hot spell.

Stratocumulus
are probably the
most common clouds.

They form a low sheet of
grey or white, rounded clouds.
The clouds can form a regular
pattern and look joined together,
but these often break up, letting
the Sun shine through.

12,000

(39,600 ft)

11,000

(36,300 ft)

10,000 m.

(33,000 ft)

Sometimes called mares’ 9,000 m .
tails, cirrus are the highest ( 29 > 700 ft)
clouds. They form in the

top of the troposphere where
it is coldest.

8,000 m.

(26,400 ft)

The engines
of high-flying
aircraft release water
vapour into the cold air.

The water vapour
condenses and freezes
making thin cloud
trails in the sky.
These are
called
contrails, from
the word
condensation.

Puffy cumulus ^
clouds occur in the
middle of the cloud layer.

They are usually grey at the bottom
but brilliant white at
the top.

Cumulonimbus clouds are sometimes called anvil
clouds. They are massive, flat-topped storm
clouds that stretch in a vertical column from about
2,000 m (6,500 ft) up to 15,000 m (49,000 ft)

above the ground.

Stratus are the lowest clouds. They
form at about 500 m (1,600 ft) above
the ground. Sometimes they are much
lower and form fog over the ground.

CLASSIFIED CLOUDS

There is a huge variety of clouds but only ten kinds are officially
classified. Different clouds form at different levels in the sky - from
sea level up to about 10,000 m (33,000 ft). Low-altitude clouds have a
base below 2,000 m (6,600 ft), medium-altitude clouds form between
2,000-5,000 m (6,600-16,500 ft), and high-altitude clouds form above
5,000 m (16,500 ft).

7,000 m.
(23,100 ft)

6,000 m.

(19,800 ft)

5,000 m_
(16,500 ft)

4,000 m.
(13,200 ft)

3,000 m.
(9,900 ft)

2,000 m.

(6,600 ft)

1,000 m-
(3,300 ft)

Sea level

Nimbostratus clouds can
cover the sky and blot
out the Sun completely
making daytime very
dark. They always bring
rain or snow. (Nimbus is
Latin for rain).

Find out more

Formation of clouds p.262
Fog, mist, and smog p.263
Rain p.264

Special effects p.269
Moon p.288

Classifying living things p.310

261

WEATHER

FORMATION of CLOUDS

The air SOAKS UP WATER from rivers, lakes, and seas like a sponge.

The water is in the form of an invisible gas called water vapour. It is this
water vapour that forms the clouds, since clouds are made chiefly of
water droplets. When the air near the ground rises into the sky, it cools
and some of its water vapour condenses (turns into drops of liquid
water). These gather together to form clouds. Air rises for several
reasons. It may rise because it has been heated up by the warm ground.

It may rise because cold air has pushed under warm air, lifting it higher.

Or it may rise to pass over hills and mountains.

As clouds get
bigger, cool air
may circulate

Warm air expands
and spreads out.

The Sun heats the ground. This
warms the air nearby and the
warm air rises into the sky.

As the air rises, it becomes cooler
and the water vapour it contains
condenses into droplets of water.
These join together to form a cloud.

As the day goes on, more and
more warm air rises and more
water vapour condenses to form
a bigger and bigger cloud.

CLOUD IN A BOTTLE
You can create a cloud in a plastic
bottle. Fill up the bottle with hot
water (don’t use boiling water
because the bottle could melt).
Leave it to stand for five minutes
and then pour away three-quarters
of the water. Lay an ice cube over
the open top of the bottle and
watch a cloud form. How does it
work? Some of the water turns to
water vapour in the warm air.
When it meets the cold area by the
ice cube, the water vapour turns
into droplets to make a cloud.

Hot

water

Ice cube

Cloud

forms

Clouds and dew

Clouds form when the water vapour in
the air is lifted high enough up into the
sky for it to cool down and condense.
The temperature at which this happens
is called the dew point. Water vapour
will turn to droplets only if the air
contains small particles, such as dust or
smoke, for it to condense on. If the air
was clean, no clouds would form.

THERMALS

’Cloud-forming is a
useful sign to glider
pilots of where
warm air is rising.
The pilots use
pockets of rising
air, called
thermals, to give
them lift. Birds of
prey use thermals to
help them stay up in
the air while they circle
round searching the
ground for food.

On the okta scale, a
vertical line across a
circle represents 1
okta. This means
there is a very fine
cloud covering.

When the sky has 4
oktas of cloud, it
means that about
half the sky is
covered by cloud.
The circle is half
shaded in.

8 oktas is the
highest point on the
okta scale. It means
that the sky is
completely covered
by cloud. All of the
circle is shaded in.

MEASURING CLOUD

Meteorologists measure the amount of clouds
covering the sky in a unit called an okta. One
okta represents one-eighth of cloud cover. The
number of oktas of cloud cover are represented
on a weather map by a partly shaded circle.

Clear sky

1 okta

2 oktas

3 oktas

4 oktas

5 oktas

6 oktas

•

7 oktas

•

8 oktas

Find out more

Cl LANGES OF STATE P.20
Forces in fluids p.128
I Ieat transfer p. 1 42
Air pressure p.250
Clouds p.260
Frost, dew, and ice p.268
Cycles in tiie biosphere p.372

262

WEATHER

Fog, mist, and smog

CLOUDS THAT FORM near the ground
are called fog or mist. Like other clouds,
they are made when the air is full of
water vapour. When the air comes into
contact with cold ground, the water
vapour condenses. If the distance
we can see through the cloud is
between one and two kilometres
(0.6 and 1.25 miles), it is called
mist. If the distance we can see
is less than one kilometre
(0.6 miles), the cloud is called
fog. A dense fog is the most
dangerous cloud. It is a hazard
to all types of transport - cars,
ships, and aeroplanes.

The light from dipped
headlights does not reflect
straight back to the driver
off droplets in
the fog.

DRIVING IN FOG
Drivers in fog have to be very
careful. Cars must use dipped
headlights. If their lights are on
full beam (directed straight
ahead), the light reflects off the
water droplets in the fog and the
driver cannot see properly.

ICEBERG FOG

Icebergs are often shrouded in fog. This is
because the air around them is cold but the
water in which they float may be warmer.
The water evaporates into water vapour,
which condenses in the cold air to form
fog. A ship called the Titanic collided with
an iceberg in 1912. The crash may have
been caused because the crew did not see
the iceberg in the surrounding heavy fog.

Radiation fog

The most common kind of fog is radiation
fog. On a night when there are no clouds in
the sky to trap heat, the ground radiates
heat so that it cools quickly. The air near the
ground then cools too. If it cools to a low
enough temperature, water vapour in the air
will condense to form fog near the ground.

Warm air above
stops fog escaping.

PEA-SOUPERS

At one time, London in England
had heavy yellow smogs, nicknamed
“pea-soupers”. This photograph was
taken in 1952. These smogs were
caused by smoke from the burning
of coal in industry and in homes.
The smog was no joke. It seeped
into buildings, causing throat, eye,
and breathing problems, and many
people died because of it. Clean Air
Acts agreed in the 1950s have made
such pea-soupers a thing of the past.

air contains
many extra particles
because of the smoke released by some
industries. Water vapour condenses on
these to form smog. This is worsened by an
effect called an inversion - a layer of warm
air prevents the surface air, and the
pollutants it contains, from rising. This can
happen in regions, such as Los Angeles,
California, in the United States, where air
is trapped by surrounding mountains.

Wind direction

ADVECTION FOG

Fog and mist often form over rivers or seas. Water
evaporates from the river or sea and early on a cold
morning, it condenses into mist over the water. When
warm air blows over a cold sea, a type of fog called
advection f og is produced. A layer of f og forms just
above the water, sandwiched between the sea and the
warm air above. Advection fog will only push inland if
the land around is low.

High land
stops fog
blowing inland.

Find out more

Changes of state p.20
Heat transfer p. 142
Reflection p.194
Formation of clouds p.262
Cycles in the biosphere p.372

263

WEATHER

0 0 0O

o o

Each raindrop
is made up of
millions of specks of
water vapour - each
one only a fraction of
a millimetre in
diameter.

0 A raindrop is shaped like a
flattened ball. It is not
perfectly round, nor is it
shaped like a teardrop.

HOW RAIN FORMS

o O

Rain

Life ON LAND DEPENDS ON RAIN. Rain fills the
rivers and lakes, it lets seeds germinate and grow, and
provides us with drinking water. In some areas, if the
rains fail for just one season many thousands of people
can die of starvation because crops fail. Too much rain
is also a problem. Floods can destroy homes, farmland,
and wildlife. Rain never falls from a clear, blue sky. It
can only form in a cloud, usually either a nimbostratus
or a cumulonimbus. Water that falls from a cloud is
called precipitation. The temperature of the air, both
O inside and outside the cloud, determines whether
precipitation is rain, snow, sleet, or hail.

O °

O ° °

Most rain outside the tropics starts off as
snow, even in summer. High up in the
clouds, the temperature is below
freezing, and ice crystals form. The
crystals grow bigger, form snowflakes,
and fall from the cloud. If the
temperature of the air nearer the
ground is above freezing, the snow melts
and turns into rain as it falls. In the tropics,
where the clouds are warm, rain is formed
when microscopic drops of water in the
clouds collide and join together. When the
drops are too heavy to stay up, they fall as
rain. In thin clouds, fewer drops collide so
the falling raindrops are smaller. Very
small drops are known as drizzle.

After
a long,
dry spell
the soil is
baked hard and
water cannot drain
away properly.

FLOODING

When there is a heavy downfall of rain, floods
may happen if the water cannot drain away
quickly. The Indian monsoon brings some
of the heaviest rain in the world and
floods the land every year, usually in
September.

Rivers burst their banks
and the surrounding flat
land can be covered
with several
metres of water.

Key to map of annual rainfall

ANNUAL RAINFALL AROUND THE WORLD

More than 3,000 mm (118 in)
2,000-3,000 mm (78-118 in)
Wm 1,000-2,000 mm (39-78 in)
500-1,000 mm (20-39 in)

\ ) 250-500 mm (10-20 in)

<_ Less than 250 mm (10 in)

Measuring

rule

Austral

uNew

Zealand

MEASURING RAINFALL
Rainfall is measured in millimetres
or inches. It can be measured with
a rain gauge. A funnel catches the
rain and directs it down into a
cylinder. The height of water in
the cylinder is the amount of rain
that has fallen.

Different regions of the world get different amounts of rain.
There are several reasons for this variation. For example, in the
tropics, there is a lot of rain because a considerable amount of
water evaporates from the warm sea and makes clouds. Land
near the sea usually gets more rainfall than land far from the
sea. Mountain ranges can block off the winds that bring rain
clouds making it wet on one side and dry on the other. And
there are dry deserts where air masses get hot and dry as they
descend towards the ground.

RECORD RAINFALL
On the top of Mount Wai-ale-ali,
on the island of Kauai in Hawaii, it
rains on 350 days a year. The
average annual rainfall is about
11,680 mm (460 in). The moist
south-east trade wind rises and
cools as it passes over the mountain
and this causes the rain.

264

WEATHER

MAKING RAIN

Clouds are sometimes “seeded” to make them
rain. Aircraft drop dry ice or silver iodide crystals
on to them. The chemicals provide “seeds” for
snowflakes to grow on. The snowflakes turn into
rain as they fall down to the ground. The effect
on the clouds where the aircraft has just sprayed
can clearly be seen in this photograph.

Vr*

Drought

If, over about two weeks, there is less
than 0.2 mm (1/100 in) of
precipitation, there is said to be a
drought. Without reservoirs, there is not
enough water for people and crops.
Some places have extreme drought
which lasts for many years. It is said that
Calama in the Atacama Desert in Chile
did not have any rain for 400 years until
1972. In temperate Europe and North
America, periods of drought are
unexpected. But in Australia and parts
of Africa, Central America, and Asia,
drought happens regularly.

Weather in the
> area under the
blocking high is
dry and settled.

Lows have
to go round
the outside of
the high.

THE DUST BOWL
During the 1930s, there
was a long period of
prevailing Westerlies
over North America. This
meant that the Great
Plains were in the “rain
shadow” of the Rocky
Mountains and had no rain.

The drought was made worse
because the farmers had
ploughed up all the natural
grasslands, letting the topsoil get
dry and dusty. The Great Plains
turned inio the Dust Bowl. Crops could
not grow and farming families were forced
of f the land.

Weather in the area away from the
high is unse^ la d.

BLOCKING HIGH

A drought can be caused by an area of high pressure blocking the passage of
moving low pressure systems. If the high pressure sticks in one place for a long
time, it can prevent any change in the weather for weeks. Blocking highs are always
dry. They bring clear, cold weather in winter and hot, dry weather in summer.

SURVIVING A DROUGHT
Flowers are blooming in this
normally dry area in Australia,
forming a pink carpet for a few
days. Most plants cannot survive in
the desert because it is so dry. But
some seeds can survive for years in
the soil. .As soon as the rains come
the seeds spring into life, flower,
and quickly set new seeds before
the ground dries up again.

does not reach
the top branches, so
they die and go brown.

There is only enough
water to keep the lower
branches alive.

THIRSTY PLANTS
Most plants need a constant
supply of water to survive. If
there is a drought, many
plants will die, even
established trees. You can tell
when trees are not getting
enough rain because their
topmost branches will die.

BUSH FIRES
In hot, dry regions, bush fires often
start. They clear the land, making
room for new plants to grow, and
the heat is necessary to make
certain seeds germinate. Where
people prevent bush fires, some
kinds of plants die out. Nowadays,
bush fires are often left to burn,
provided that they do not threaten
people’s lives.

Find out more

Cycle*

Clouds p.260
Snow p.266
Hail p.267

> IN THE BIOSPHER]

Deserts p.390
Fact cixder p.416

e p.372

265

WEATHER

Snow

Ice caps have a shiny, white
surface that reflects the Sun’s
heat. This helps to keep them
cold even during the summer.

tea*

No TWO SNOWFLAKES are exactly the
same. Each one is a collection of ice
crystals, made of frozen water vapour, frozen
together. Ice crystal shapes are divided into
about 80 categories. They can be shaped
like needles, prisms, plates, hexagons, and
columns. The shape depends on the
temperature, height, and water content of the
cloud in which they form. Snow can be “wet” or
“dry”. Wet snow is made of large snowflakes and
forms when the temperature is just about

freezing. It is perfect for making snowballs
but difficult to clear away. Dry snow is
powdery and easy to clear. It forms when the
temperature is well below freezing. Sleet
is usually half-melted snow, but it can be
half-frozen rain formed when raindrops
evaporate and cool as they fall.

PERMANENT SNOW
Glaciers and ice caps are
made from snow that
has never melted.

Instead, all the crystals
and snowflakes have been
squeezed together by the
weight of more snow
falling on top. Ice caps and
glaciers form on mountain
tops and near the Poles.

SNOW DRIFTS
When snow builds up in drif ts,
people can get stuck in cars or even
inside their homes. If animals or
people get buried in snow, they can
survive for a long time. This is
because freshly fallen snow contains
air in the gaps between the ice
crystals which the animals
can breathe.

AVALANCHES

If a mountain slope is steeper

than 22°, avalanches can happen.

The snow piles up until a small
amount starts to slip, collecting more
and more snow as it goes down the
slope. Avalanches may be set off by a
heavy fall of snow on ice, a rise in
temperature, a skier, or even by a loud
noise.

How SNOW FORMS

Ice crystals form in clouds where
the temperature is between -20 °C
and -40 °C (-4 °F and -40 °F). To form snowflakes, the crystals
join together as they fall and become wet, and then re-freeze.
When they fall out of the cloud, they will reach the ground as
snow only if the temperature of the air is freezing all the way
down. If it is too warm, the crystals may evaporate back into
water vapour or melt and fall as sleet or rain. Sometimes, it
can be snowing on the top of a tall skyscraper, while it is
raining in the street below.

PINK SNOW

Snow is not always
white! It can be pink,
brown, or even red.
This pink snow is in
Greenland. The colour
is caused by algae
living in the snow. The
pigment that makes
the algae red also
protects them in the
extremely cold
conditions.

All snowflakes form
in a six-sided
symmetrical pattern.

Find out more

Heat transfer p.142
Ice and glaciers p.228
Temperature p.251
Clouds p.260
Polar and tundra lands
p.382

266

WEATHER

New layer of ice freezes
around the hailstone.

HAIL

Hailstones are frozen drops of

rain. They form inside tall
cumulonimbus clouds which are much
warmer at the bottom than at the top,
where it is freezing. The temperature
difference causes strong currents inside
the cloud. These currents toss the
raindrops up to the freezing top of the cloud
and down again. In order for a hailstone to stay
up in a cloud long enough to become even pea¬
sized, it needs to be swept up and down at
speeds of about 30 m (100 ft) per second. As
hailstones rise and fall inside a cloud, they
crash into each other often causing electric
charges to separate out and make
lightning. Even when the hail is not
falling to the ground, it can still
make lightning inside the clouds.

The hailstone eventually becomes
too heavy to be held up in the cloud
and it falls to the ground.

Current of air takes the

hailstone back up to the top of the cloud.

How HAIL FORMS

Hailstones develop inside cumulonimbus clouds which have
grown to a height of about 10 km (6 miles). Strong,
uprising air currents within a cloud can lift raindrops up
into the frozen cloud top. The first time this happens the
raindrop freezes and falls. When it is tossed upwards again a
further layer of ice builds round it. The ice builds up, layer
upon layer, until the hailstone finally falls to the ground.

LAYERS OF ICE
This cross-section of a
hailstone clearly shows
that a hailstone is
made in layers, like
the layers of an onion.
Each layer represents one
y journey up to the top of a
storm cloud and back down
to the bottom.

RECORD HAILSTONES

Hailstones are often as big as
marbles, and sometimes as big as
tennis balls. Less common are
those that fell in Bangladesh in
1986. They weighed 1.02 kg (2.25
lb). Shown here is a giant hailstone
which fell in Kansas in the United
States in 1970. It measured 43.6 cm
(17.2 in) in circumference and
weighed 765 g (1.7 lb).

HAIL DAMAGE
Hailstones can cause severe damage.
They ruin crops, such as these apples,
making them unfit to sell. Large
hailstones can break windows and dent
cars. Small birds, caught in a storm with
no cover, have been killed by hailstones.

HAIL PREVENTION
Many attempts to prevent
hail damage have been
made, including firing guns
4nto the clouds, as shown
by this French magazine of
1910. More recently, silver
iodide crystals have been
fired into clouds. It is hoped
that this will turn the
hailstones into rain. But there
is no proof that this works.

Find out more

Sta

Thi

EAT TRANSFER P.14

TIC ELECTRICITY F.

JNDER AND L1GHTN
p.257

Clouds p. 260
Rain p.264

146

UNO

267

WEATHER

Frost, dew, and ice

When the SUN HAS SET at night, the ground begins to lose its heat.
The air does not lose heat so fast so the ground becomes colder than
the air above it. On a clear, still night, water vapour in the air condenses
on the ground as dew drops. The temperature at which dew starts to
form is called the dew point. If the temperature of the air falls below
freezing, the water vapour turns into ice crystals and coats everything
with frost. Sometimes, a layer of transparent ice forms on the ground
making roads slippery. It happens when rain falls through very cold air
on to ground that is below 0°C (32°F), where it freezes into “black” ice.

It is called black because the road can
be seen through it.

DF.W POND

Dew that forms at night covers the
ground in the early morning.
When the Sun comes up, and it
begins to get warmer, the dew
evaporates into the air. Some
farmers make dew ponds - hollows
in the ground in low-lying parts of
a field. Dew runs down and
collects in the dew ponds for
animals to drink first thing in the
morning. Sometimes dew 7 ponds
occur naturally.

Frozen
water forms
a dome.

Water
expands
through the

Hoar frost

Frost usually occurs
on a cold night
when there is no
blanket of cloud
to stop warmth
escaping from
the ground. The
most usual kind
of frost is hoar
frost. This coats
the ground,
leaves, branches,
and even spiders’
webs with a thin layer
of tiny ice crystals.
Sometimes hoar frost is
so white and so deep on the
ground that it looks like snow.

Water freezes
to form an “icicle”.

“UPSIDE-DOWN” ICICLES
Sometimes “icicles” form in shallow
puddles or bird baths - sticking up. This
happens because water expands when it
freezes and pushes up a little dome of
ice. If this cracks, water from underneath
the dome pushes up through the crack
and freezes. When this happens several
times, the result is a spike of ice.

FROZEN WATER

If it is very cold, a layer of ice can form over rivers and
lakes. This ice may seem strong and thick at the edges,
but there will be w r eak spots where the ice is thinner.
That is why it is dangerous to walk on water that
is covered with ice. Fish survive because the ice
acts like a lid, stopping the water underneath
from freezing.

It is unusual for the ice on a river or
lake to be thick enough to skate on.

FROZEN SEA

Seas do not often freeze because salt
water freezes at a lower temperature
than fresh water does. But if it is
cold enough, ice can cover the sea,
especially near the coast.

ICEFISH OF ANTARCTICA

The waters around
Antarctica are so cold that
they would freeze the blood
of ordinary fish. Fish that
live in these waters have
evolved chemicals in their
blood that act as a natural
“antifreeze” - just like the
antifreeze put in a car to
stop the water freezing in
the winter.

Find out more

Changes of state p.20
Heat transfer p.142
Ice and glaciers p.228
Snow p.266

POIAR AND TUNDRA IANDS
p.382

268

WEATHER

Ray of light

Raindrop

HOW

SUNLIGHT IS SPLIT
A ray of light passing through a
raindrop is bent on its way in and
on its way out. It is also reflected
of f the inside of the raindrop.

If there is a second rainbow,
the colours are reversed.

Special effects

The COLOURED PATTERNS of a rainbow or a
glorious sunset are familiar to everybody. But the
changing patterns of weather can play other
strange tricks on us. They produce pillars of light
in the sky, rings around the Sun and Moon, and
strange distortions of the shape of the Sun as it
sets. The way stars twinkle in the sky has nothing
to do with the stars themselves, but is caused by
the effect of the air on light passing through it.

And the atmosphere can
even bend light, to
bring you an
image of a
far-distant
object.

igr

ST ELMO’S FIRE
In stormy conditions, an electric
discharge, like lightning, may form
a bluish-green ball of light on
pointed objects. One of these on a
ship’s mast was known to sailors as
St Elmo’s Fire. It is sometimes seen
today on the wingtips of aircraft,
or lightning conductors.

Rainbows

You can see a rainbow only when the Sun is shining behind
you and it is raining in front of you. Rainbows form when
sunlight shines through millions of raindrops. Sunlight is a
mixture of colours. When it passes through a raindrop, it is
refracted (bent) and the light splits and spreads out into
seven colours. All rainbows are part of a circle, but you can
usually see only part of it, as the Earth is in the way. If you
are lucky, you may see a complete circle from an aircraft.

The colours of a
rainbow are, from
the outside inwards,
red, orange, yellow,
green, blue, indigo,
and violet.

MIRAGES

Mirages are associated with hot deserts, but you
may see one on a hot road. Light bends from
warmer air towards colder air. When air near
the ground is hotter than air above, light rays
are bent up so that they come to the eye from a
different place to where they started. It can
look as if there is a lake ahead, but this is really
an image of the sky. You see light rays from the
sky coming from near the ground.

JOHN TYNDALL

Irish scientist
John Tyndall
(1820-93) studied
glaciers and was
one of the first
people to climb
the Matterhorn
mountain in the Swiss
Alps. He studied light
and how it is scattered by large
molecules and dust. This effect,
known as the Tyndall effect, is the
cause of shafts of sunlight. Tyndall
suggested that the sky is blue
because the blue part of sunlight
is scattered more easily around
the sky than other colours. This
was later proved by Einstein.

HALOES AROUND THE MOON

When light from the Moon passes through ice crystals high
in the sky, haloes sometimes form around the Moon. Light
reflecting off the ice cry stals is bent at angles of either 22°
or 46° to make two separate haloes. The haloes are often
incomplete, and usually only the smaller one can be seen.

Haloes around the Moon

BROCKEN SPECTRE
An unusual effect can
be seen, especially in
mountains, when the
Sun is low in the sky. The
Sun casts a large shadow of
objects or people on to
low-lying mist or clouds.
The shadow is called the
Brocken spectre after
the Brocken mountain
in Germany.

Find out more

Static electricity p.146
Refraction p.196
Tight and matter p.200
Shadows p.201
Colour p.202
Atmosphere p.248

269

WEATHER

VIEW FROM SPACE

Photographs of clouds are taken from space by weather
satellites. They show at a glance what the weather is
like. This satellite picture shows the cloud patterns
associated with the weather chart above. The cloud forms a
dense knot near the centre of the depression, with more
cloud spreading out along the line of the front.

"Arrow” indicates direction
of wind; “feathers” indicate
the strength

Thick cloud in the
depression, bringing
rain and snow

Chart for Japan

Forecasters draw up weather
charts to show the picture of what
conditions such as temperature, wind,
pressure, and rainfall are like. They
use internationally agreed weather
symbols. This chart for 16 December,
1992 shows a developing low pressure
system, or depression, over japan.

Strong winds sweep anticlockwise
around the low, swinging warm and
cold fronts around with it. Japan has
wet windy weather, while, to the west,
high pressure means that the weather
over China is cold and dry.

front

High pressure
brings clear air with
no precipitation.

A weather sign for
thunder marks
the battle

site

WEATHER IN HISTORY
Using old records, experts can
draw up weather maps, or charts,
for days in history. This map is of
the night before the Battle of
Waterloo, 17 June 1815. The
battle was between the armies of
the French emperor Napoleon
and the Allied army commander
the Duke of Wellington. Heavy
rain made the ground muddy
and delayed the French attack.

This gave time for more troops
to reach and support

Wellington’s army which
won the battle.

Occluded front

White

triangle indicates
showers indicates

rain

FORECASTING

What is the weather going to be like today? To forecast
the weather accurately, information must be gathered from all
round the world. There are two types of forecast - long-range
forecasts predict the weather for up to five days ahead; short-
range forecasts predict the weather for the next 24 hours. The
biggest non-military customers for weather forecasts are civil
aviation organizations, such as airlines and airports, which need
to know conditions at different altitudes. Shipping needs to be
warned of storms; power stations need to know if it is going to
be cold, so that they can estimate the demand for energy.
Farmers need forecasts so they can plan harvesting and protect
crops. And you want to know what clothes to wear, or whether
to take an umbrella out with you even if the Sun is shining!

Circle indicates
cloud

Depression
moving slowly
east, bringing
heavy rain to the
Waterloo area

Star indicates
snow _

Isobar joining
areas of equal
pressure

No arrow
indicates
calm

270

WEATHER

SATELLITES
Information from Earth is collected by
satellites and sent down to
weather stations every
30 minutes, with
photos of cloud
patterns.

Collecting information

The World Meteorological Organization (WMO) has 150
member countries that share information in the World
Weather Watch. Data from nearly 10,000 land stations,

7,000 ships, hundreds of aircraft and balloons, and several
satellites are gathered each day at centres in Moscow in
Russia, Washington DC in the United States, and Melbourne
in Australia. Regional and worldwide forecasts are

made and sent to members of the WMO. These send
the data to national weather offices, which make

the forecasts for their
own countries.

LEWIS FRY RICHARDSON

British mathematician
LF Richardson (1881-1953)
worked out how to use
mathematical techniques to
forecast the weather. He worked
on his theory while serving in the
ambulance corps during the First
World War. His manuscript was lost
during a battle in 1917, but it turned
up several months later under a heap
of coal. Richardson’s work was published
in 1922, but his ideas could not be used until the
electronic computer was invented twenty years later.

AIRCRAFT
Specially adapted
aircraft carry
instruments up into
the atmosphere. The
measurements are
sometimes immediately
beamed back to the
ground, and
sometimes recorded
and brought back.

SMALL STATIONS
Individuals with a
few simple
instruments play an
important part in
weather forecasting.
They send their
information about
local conditions to a
main weather station.

SHIPS

Weather ships take measurements of pressure and
temperature at sea level, and they measure the temperature
of the sea itself. They launch weather balloons which send
back information about the atmosphere at
different heights.

USING FORECASTS
Airports need forecasts of bad
weather so that equipment can be
made ready to keep the runways
open. Snow and ice are the worst
hazards, but warnings of strong
winds are also important.

AUTOMATIC BUOYS
Weather buoys arc used in
place of crewed ships.
They record information
about the local
weather at sea level.
The information
is collected by
satellites.

COMPUTERS

Information from around the world
is fed into computer “models”.
The computers help make
forecasts of future weather.

RADIOSONDES
Helium-filled balloons carry
packages of instruments,
known as radiosondes, into the
atmosphere. As well as sending
back temperature and pressure data, the
radiosondes are tracked to show wind speeds.

Radiosondes are
released at least
twice a day.

AUTOMATED STATIONS
Weather information in remote
regions is collected at unstaffed
stations. The information is sent
automatically via satellite to the
forecasting centres. Similar stations
are set up on some offshore oil rigs.

Find out more

Air pressure i\250
Fronts p.253
Wind strength p.256
Formation of clouds p.262
Weather watching p.272
Satellites p.300
Factfinder p.416

271

WEATHER

P®

WATCHING

FOR THOUSANDS OF^EARS, before.weatirer^recording
instruments were invented in the 16th century, people had to
study natural signs to know what weather was coming. As well as
the sky and clouds, animals, plants, the Sun, and the Moon all had
their part to play. Many sayings arose from the signs and are now
part of folklore. There are, of course, different signs and sayings in
different parts of the world. Many of these are more than folklore
- they work. Careful weather watching,
combined with simple measurements of
temperature and pressure, makes do-it-
yourself local forecasting very reliable.

The screen shades instruments *

from the Sun’s direct heat. But
louvred sides allow air to ^

circulate through the box.

RED SKY

The sfcvWred even- dawn and dusk. But when it

is c loudy the sky’s colour is hidden. In Europe
and North America, winds usually bring weather
f rom the west. If plenty of red sky is seen when
the Sun is setting in the west, it means clear
weather is on its way. Red sky in the morning
means the good weather is on its way out.

Double roof keeps

_ the Sun off.

Wet- and
dry-bulb
thermometers

JAPANESE
CHERRY
In Japan, the dates
on which the
cherry trees
blossom have been
recorded for centuries.
The records help weather watchers to
know what the weather was like hundreds
of years ago, and whether there was a
harsh winter or an early spring in any year.

The bulb of one
thermometer is
kept wet in
distilled water.

As the water
evaporates, heat
is taken from the
thermometer.

All Stevenson
screens stand
at 1.2 m (4 ft)
high, so records
from them all can
be compared
accurately.

Stevenson screen

Most weather stations and many schools have a Stevenson
screen. This may contain a wet- and a dry-bulb thermometer
to record humidity. The wet and dry thermometers show
different temperatures according to the humidity. The
humidity is worked out from a scale. There may also be a
maximum and minimum thermometer and chart recorders

SEAWEED

A piece of seaweed brought back from the
such as this kelp, can help you to observe
changes in the weather. When the weather is
dry 7 , the moisture in the seaweed evaporates, leaving it
brittle and hard. In humid weather, the seaweed absorbs
moisture from the air and it becomes plump and soft again.
Seaweed changes tell us about the weather that we are
having now, rather than what is coming.

of humidity and temperature.

COWS

It is popularly thought that if cows lie Human knee

down it means that rain is coming. The
cows are supposed to be ensuring they
have somewhere dry to lie. Even if
this is true, cows lie down at all sorts
of times. So a field full of cows lying
down doesn’t always indicate rain!

The seaweed
feels damp
when rain
threatens.

Animals
suffer rheumatism
—in their joints.

BONES

During spells of mild weather,
people who suffer from
rheumatism can be quite free
of pain. But when cold, damp
weather is on its way they can
“feel it in their bones”.

Find out more

Light and matter p.200
Changing climates p.246
Air pressure p.250
Temperature p.251
Humidity p.252
Clouds p.260
Special effects p.269
Forecasting p.270

272

SPACE

Lookup into the sky and you are looking out into space. You can see
stars and planets, as well as vast expanses of empty space in between. From
the earliest times, people have tried to understand how we on Earth fit into
our local part of space, and into the rest of the Universe that lies beyond.
Early civilizations used the movements of objects in the sky (celestial
objects) as a calendar, as a means of navigation, or to predict events
in their lives. Early astronomers (people who study objects in
space) tried to explain the movements of the celestial objects.

Since the 19th century, they have tried to explain what the
objects actually are. Today, astronomers have the most
sophisticated technology available, which they use
on Earth and in space, to pursue their quest.

In 1609,
the Italian
astronomer
Galileo
Galilei was
the first
person to
make a
study of the
skies with a
telescope.

When Galileo studied the Moon with his telescope, he saw
craters and mountains that were invisible to the naked eye.

PHOTOGRAPHS OF SPACE
For centuries, the only way to learn
about the Universe was to collect
and study the light waves given out
by objects in space. Today,
astronomers are able to collect
and examine other types of
radiation that are given out, such
as X-rays, to build up a more
complete picture of the Universe.

This X-ray photograph of the leftovers
of a supernova (exploding star) reveals
clear, bright details. A photograph that
captured only light waves would have
shown just a dimly glowing gas.

Galileo’s

telescope

TELESCOPES

Technology has had a big effect on astronomy. In the
early 17th century, the newly invented telescope was
First used to look at the sky. It revealed spots on
the Sun’s surface, four of the planetjupiter’s
moons, and countless more stars. Since
then, the telescope has become more
powerful and sophisticated.

Modern telescopes are used
to measure star positions,
take photographic
images, and to
analyse star
light.

The regions of redare
where most X-rays are
being given out.

X-ray image of
Cassiopeia A
(supernova
remnant)

Lonely space

The Universe is full of billions of stars and galaxies,
but it is still a very empty place. The Universe is so vast
that even the light from all the billions of stars doesn’t
illuminate it. In between the stars are billions of
kilometres of empty, cold, and dark space. The only
known intelligent life-form in the Universe is human.
For humans, space is a very lonely place indeed.

Between them, two space probes called
Voyager visited the planets Jupiter, Saturn,
Uranus, and Neptune over the period 1979-89.
They confirmed some scientific theories, but
also made some unexpected discoveries.

MODERN EQUIPMENT
Astronomers not only use
equipment on Earth, they also send
it into space to get a better look at
our surroundings. Telescopes in orbit
around Earth can see objects in
space more clearly and can pick
up radiation that cannot
penetrate Earth’s
atmosphere. Robots
called space probes
are sent on lonely
journeys to fly around and
land on other planets,
sending their discoveries back I
to Earth. Most telescopes and
space probes are controlled
from Earth by computers.

273

SPACE

Universe

The UNIVERSE IS EVERYTHING you can think of, and more
besides. It includes all the stars, planets, moons, animals,
plants, books such as this one, and you - it even
includes all the empty space in between. Early people
thought that the Universe only contained what they
could see with their eyes from Earth. They thought
of Earth as the central and most importa'nt part of
the Universe. Today, we knowjust how vast the
Universe is, and what a tiny part of it the Earth
makes. Our present understanding of the
Universe has been developed by astronomers
and cosmologists working this century.

Astronomers study specific parts of the
Universe; cosmologists strive to explain the
Universe’s origin and development.

Changing universe

Everything in the Universe is changing. On Earth, humans or
plants change as they live out their lives; stars in space have
lives too, so they are also continually changing. Even the
Universe as a whole does not stay the same. It too has a life of
its own. Early this century, astronomers discovered that all
galaxies (enormous collections of stars) are rushing away
from each other. The Universe is getting bigger.

LIGHT YEAR

Distances in the Universe are so vast that a
light year is used to measure them. This is the
distance a ray of light travels in one
year. As light travels at 300,000 km
(186,000 miles) per second, it
covers 9,460,000 million km
(5,870,000 million
miles) in one year.

Humans

Humans make up a tiny
fraction of the Universe.

Solar System

Earth is one of
nine planets that
travel around a
star called Sun.

RED SHUT

Light travels as a wave. A squashed-
up light wave is blue. A stretched-
out light wave is red. In between are
all the other colours of the

Earth

Humans live on a
planet called Earth.

The speed of light is the universal
speed limit. Nothing can travel faster.
Even so, the light from the nearest star
to us (apart from the Sun) takes 4.3
years to reach us. It is 4.3 light years
away. We see this star as it was
4.3 years ago.

Milky
Way

The Sun is
just one of
around 200,000
million stars in a
galaxy called the
Milky Way

Astronomers
believe there
are millions of
stars in the
Universe with
their own
planets. So far,
only six are
known, including
our Sun.

Universe

In all, there are around 100,000
million galaxies in
the Universe.

Cluster of galaxies

The Milky Way lives in a
cluster of about 30 galaxies.
Such clusters of galaxies are
loosely grouped into
superclusters.

EDWIN HUBBLE

In 1924, an American astronomer,
Edwin Hubble (1889-1953), showed
that nebulae (fuzz) 7 light
patches in the sky) were
distant galaxies. In 1929,
he found the speed a
galaxy moves away
from Earth depends
on its distance from
Earth. If a galaxy is
five times as far
away as another, it is
moving five times as fast.

This is Hubble’s law.

spectrum. The light from a galaxy
moving away from us will be
stretched towards the red end of
the spectrum. This is called a red
shift. It will be more red-shifted if
the galaxy is moving faster. From
Hubble’s law, astronomers know
that the more distant galaxies move
away faster than closer ones. The
red-shift therefore shows how far
away the galaxy is.

The orange-red light from this galaxy
shows it is moving away from us.

The light from this galaxy is shifted further towards the red
end of the spectrum. This shows us that the galaxy is
moving faster and is farther away than the galaxy above.

Find out more

Measuring sound i\180
Light i\190

Origin of the universe p.275
Gaiaxies p.276
Stars p.278
SOIAR SYSTEM P.283
Study of astronomy p.296

274

SPACE

Find out more

Ici

OMIC STRUCTURE P
£ AND GLACIERS P.2
Universe p.274
GATAXIES P.276
Stars p.278
Satellites p.300

.24

Origin of the universe

Most SCIENTISTS THINK THAT the Universe was born in
a colossal explosion called the Big Bang. In this explosion,
13,000 million years ago, all matter, energy, space, and time
were created. Of course, no-one was there to tell us what
happened. But discoveries in physics and astronomy
have enabled scientists to trace the Universe’s history
to its first fraction of a second. They believe at that
time, the Universe was squashed into a tiny volume,
and it has been expanding ever since. The Big Bang
Theory was put forward in 1933. Another idea, called
the Steady State Theory, was suggested in 1948. This
said that new material was continuously being
created, and so overall the Universe would not
change. The Steady State Theory has now been
discounted. More recently, scientists have been looking
into the future of the Universe. What happens next?

Big bang

Around 15,000 million years ago, the Universe was
very small and very hot. An explosion, the Big
Bang, started of f the process of expansion and
change which still continues today. Within minutes
of the explosion, atomic particles came together to
make the gases helium and hydrogen, which over
millions of years produced the galaxies, the stars,
and the Universe as we know it today.

BOUNCING UNIVERSE

What will happen to the Universe? Scientists have diff erent views about this.
Some think it will have no definite end, but will gradually run down. This is the
open Universe theory. Others think that it will stop expanding and start to
contract until it is compressed and hot once
more. This is the closed Universe theory.

The Sun was born 8,000 > 45 v

million years after the Big /^S, The first life forms appeared on Earth

Bang. The Earth and planets f j % „ abou < 10 - 000 m "" on T ears

evolved from the debris. t.

after the Big Bang.

The Universe may

The Universe started
expand as a result
of the Big
Bang.

- Big
Bang

The Cosmic
Background
Explorer (COBE)
satellite investigated the
radiation from the early
Universe. In 1992, it detected
unevenness in this radiation -
the first signs of galaxy-birth.

BACKGROUND RADIATION

From the 1940s, scientists studied
what the very young Universe
was like. They realized it must
have been full of radiation. As
the Universe grew and cooled,
the radiation would have cooled
too. Russian-American scientist
George Gamow even worked
out the temperature that it
should now be. In 1965, two
American scientists, Arno
Penzias and Robert Wilson,
detected exactly this type of
radiation (called the background
radiation). It provided evidence
for a Big Bang.

Our Galaxy, the Milky Way, formed
into a disc shape 5,000 million
years after the Big Bang.

Dinosaurs lived 190
million years ago.
Humans have been
around for just 2
million years - a tiny
fraction of the
Universe’s life.

The present
time is around
13,000 million
years after the
Big Bang.

3,000 million years after
the Big Bang, galaxies
started to take shape.

1,000 million years after
the Big Bang, material
started to come together.

TIMELINE

When the Universe was born, it was
more.or less the same throughout.
As it expanded, material inside it
clumped together.

Gravity drew more and
more material together,
leaving regions of
empty space in
between. The
regions of material
eventually gave birth
to stars and galaxies.

In minutes, the
Universe was
made of 75%
hydrogen and
25% helium.

The temperature
was over 10,000
million degrees.

2-3,000 million years
after the Big Bang,
quasars
(forerunners of
galaxies) evolved.

275

SPACE

IRREGUIAR

Irregular galaxies are those that
have not formed into a specific
shape. They are the rarest type
of galaxy in the Universe.

CLUSTERS

Galaxies tend to stick together. They are spread
throughout the Universe in clusters. The Milky Way is
in a cluster of about 30 galaxies called the Local Group.
Other clusters can contain thousands of galaxies.
Clusters may group together into superclusters.

Irregular

galaxy

M82

JGC 5194

spi

JM ' Ik s

Part of the Virgo cluster of
galaxies, the nearest major
cluster to our Local Group.

SPIRAL

Spiral galaxies contain
young and old stars.
They are disc¬
shaped with spiral
arms. In a barred
spiral, the arms
come out from the
ends of a bar across
the centre of
the galaxy.

Galaxies
start their
lives as
giant clouds
of gas. The
cloud spins,
stars start to form,
and the galaxy takes
shape. The faster the
spin, the flatter the galaxy.

ELLIPTICAL

Elliptical galaxies are flattened
ball-shaped collections of old
stars (stars at the end of their
life). They are the most common
type of galaxy in the Universe.

M49 elliptical galaxy.
It has a diameter of
50,000 light years.

QUASARS

In 1963, a new category of object
- the quasar - was identified. We
know these are very luminous,
distant objects, moving away from
us at great speed. I lowever, many
questions about them remain
unanswered. At present, they are
thought to be the cores of very
young galaxies.

Distant worlds

By the start of the 20th century, astronomers had listed
large numbers of dim, fuzzy patches in the sky which
they called nebulae. Many of these had been seen for
centuries. Some people thought they were just
clouds of gas in the Milky Way. Others thought they
might be distant galaxies. And indeed this is what
many turned out to be. American astronomer
Edwin Hubble studied them and classified them
according to their shape. There are four main types
of galaxies - spirals (like the Milky Way), barred
spirals, ellipticals, and irregulars.

Radio image of
quasar 3C 273. Its
core (top left) and its tail
(bottom right) are powerful
emitters of radio waves.

Galaxies

OTHER GALAXIES
In 1924, the
American
astronomer Edwin
Hubble proved the
existence of other
galaxies. He
showed that stars
within the
Andromeda
Nebula (later called
the Andromeda
Galaxy) were too
distant to be members
of the Milky Way.

Stars live together in “star cities” called galaxies.

These enormous collections of stars started off as huge clouds
of gas soon after the birth of the Universe. Gravity eventually
pulled the gas into separate stars. Galaxies are so vast that it
takes starlight hundreds of thousands of years to travel from
one side to the other. The way the stars are arranged within a
galaxy gives it a distinctive shape. Our star, the Sun, lives in a
spiral-shaped galaxy called the Milky Way. Up until this
century, astronomers thought that the Milky Way Galaxy was
the only galaxy in the Universe. Today, we know it is just one

of 100,000 million
galaxies that
exist.

276

SPACE

Milky way

The Milky Way is a spiral galaxy with a
concentration of stars at its centre. This gives
the Galaxy a central bulge from which arms
of stars radiate out. We live in one of
these arms. This means that from the
Southern Hemisphere of Earth, we look
in towards the centre of the Galaxy;
from the Northern Hemisphere, we
look out to its edge. Like all galaxies,
the Milky Way is moving. Not only is the
whole galaxy travelling through space,
but the stars within it are continuously
moving around the galactic centre

Photograph of Milky
Way taken from
New Zealand

Milky Way -
view from
above

Milky Way -
side-on view

, -rvVS

All the stars you can
see in the night sky belong to
the Milky Way. Sometimes, you can
see a milky path made from the light
of the Galaxy’s millions of stars.

Stars don’t stay in the
same position within the
Galaxy. Over long periods
of time, they move in and
out of the spiral arms.

It would take a ray of
light 100,000 years to
travel from one side of
the Galaxy to the other.

The Sun takes
around 220 million
years to make one
journey around the
galactic centre.

SUN’S POSITION

Our Sun lives in one of the Milky Way’s spiral arms, about two-thirds
from the centre. It is just one of the estimated 200,000 million stars
that make up the Galaxy. There are stars that live in between the
spiral arms, but because the stars in the arms are younger and
brighter, it is these that give the Galaxy its distinctive shape.

Photograph of light
released from the
Andromeda
(M31) Galaxy.

This is the
closest major
galaxy to our own.

William
Herschel’s
model of
stars in the
Milky Way

Origin of the Milky Way by Tintoretto

MYTHICAL ORIGIN
The Milky Way is so-called because it looks like a splash of milk
in the night sky. In Ancient Greece, long before people
understood the nature of the Milky Way, they explained that the
Milky Way originated from milk spilt as young Hercules drank
from the goddess Juno’s breast.

HERSCHEL’S MODEL
In the 18th century, the British
astronomer William Herschel
(1738-1822) surveyed the stars
in the Milky Way. With the naked
eye, you can see around 6,000
stars; with a telescope, you can
see many millions - far too many
to count. Herschel decided to
count certain areas of stars and
then average out the results.

In this way, he made a fairly
accurate model of the Milky Way.
He also proposed that some
nebulae might be star systems
outside our own Galaxy. It was
more than a century later before
he was shown to be correct.

VIEWING GAIAXIES
To build up a more complete picture of
our Universe, we can gather other types
of radiation from it as well as light. For
example, X-ray views will show up very
hot regions of energetic activity.
Gamma-ray views reveal regions in
which energy is released from nuclear
reactions. Other wavelengths can pick
out concentrated areas of hydrogen gas
between stars and areas of cold dust.

Infrared image of the Andromeda
, Galaxy. These infrared rays have
travelled for 2.2 million years
before they reach Earth.

An X-ray image of the
Andromeda Galaxy. The
bright region in the centre is
the core of the galaxy (the part
that releases the most X-rays).

Find out more

Universe p.274
Stars p.278

Life cycle of stars p.280
Constellations p.282
Sun p.284
Uranus p.292
Telescopes in space p.298

277

SPACE

Stars

STAR SPECTRA
Astronomers use special
equipment to collect and then
separate a star’s light into its
spectrum. On the spectrum are
dark lines called absorption
lines. These show which
elements the star contains.
Every star gives a different
spectrum. An American
astronomer called Annie Jump
Cannon sorted the spectra of
thousands of stars into
different types. Each type is
given a letter of the alphabet.
The main types are O, B, A, F,
G, K, M, where each star type is
cooler than the previous one.

The gaps, or absorption lines, in
a spectrum show which types of
light the star has “used” or
absorbed. This is an indication of
which elements the star contains.

Core of star where
nuclear reactions occur

CECILIA PAYNE-
GAPOSCHKIN

In the 19th century, the
English astronomer
William Huggins
showed that stars are
made of the same
elements that exist on
Earth. In the 1920s, a
British astronomer
named Cecilia Payne-
Gaposchkin (1900-79)
proved that stars are made
mostly of hydrogen. She also
found that the make-up of most
stars is the same. These were great
discoveries that made her a
pioneer of stellar astrophysics (the
study of the physical and chemical
processes in stars).

Energy is released
at the surface as
light and heat.

Inside a star

Most stars, such as our Sun, are
made almost entirely of two gases,
hydrogen and helium, with very
small amounts of other elements.
The gases are compressed in the
centre of a star which becomes very
dense and hot - so dense and hot that
nuclear fusion reactions occur here:
hydrogen atoms combine to form helium,
mass is lost, and energy is released. This
energy travels from the core to the surface of
the star, where it is let loose as light and heat.

Energy released from the core is carried
through the star by convection and radiation.

A measurement is
taken of the star’s
position when the

Gravity pulls the gases A star's temperature
inwards; light and pressure and density increase
push them outwards. towards the centre.

Sun

is taken of the star’s
position when the
Earth is here.

The nearby star moves against the
background of more distant stars.
The more it moves, the closer it
must be to Earth.

A star is made of
gas throughout.

Instruments such as
spectrometers contain
prisms which split
the light from a star
into a spectrum
which can be
analysed.

Background
stars. Because
they are so far
away from Earth,
they appear not
Nearby to move,

star

PARALLAX
If you hold your finger in front of
you, and look at it first with just
your left eye and then with just
your right eye, your finger shifts
position against the background.
The closer your finger is, the
bigger the shift. The shift is a
measure of the distance between
finger and eye. This effect is
known as parallax and, on a
much grander scale, it can be
used to calculate the distances of
nearby stars. As the Earth orbits
around the Sun, a star will appear
to move slightly against the
background of more distant stars.

This produces a parallax angle
which can be used to measure the
distance of the star from Earth.

EVERY ONE OF THE STARS you can see in the night sky is
actually a violent, spinning ball of hot, luminous gas. The gases of a
star are held together by gravity. Stars get their energy by
“burning” their gases. This is not like burning coal, but it is a more
efficient reaction called nuclear fusion. The amount of gas a star
contains is very important as it influences the gravity, temperature,
pressure, density, and size of the star. Stars live in galaxies and each
galaxy contains many different types of stars. Astronomers have
only understood the true nature of stars over this century. Until
then, they were more concerned with the positions of stars.

278

SPACE

Main sequence stars

Stars at the top of the main
sequence have 60 times the
Sun’s mass. Those at the
bottom have just one-twelfth
the Sun’s mass.

This blue-white star is a B-type,
with a temperature of about
20,00FC (36,00FF).

White stars are classified
as A-types, with a
temperature of about
10,000 P C (18,000 P F).

Blue giants are very bright and very hot
stars. They are O-type stars with a
temperature of around 35, OOFC (63,OOFF).

The spectral types of stars, O, B, A, F, G, K, and M, relate to the star’s colour
and temperature. O-type stars are blue and hot, M-type stars are red and cooler.

Main sequence stars

The colour of a star gives us an idea
of its surface temperature. Blue stars
are hot; red stars are cooler. If the
temperature is plotted on a graph
against the star’s absolute magnitude
(how much light it releases), most
stars fall within a narrow band called
the main sequence - the hotter the
star, the brighter it shines. All stars
on the main sequence are in a stable
time of their lives - they are shining
steadily because they are fusing
hydrogen in their cores. When the
hydrogen fuel has been used up, the
star will move off the main sequence.
More massive stars will move off
more quickly than less massive stars.

This yellow-white
star is an F-type
star, with a
temperature
of about
7,50FC
(13,50FF).

Bright stars

Absolute

magnitude

Dim stars

JEWEL BOX
Most stars look like silver
pinpoints of light in Earth’s sky.
But we can see the true colour
of some stars. This colourful
group of brilliant stars is called
the Jewel Box cluster.

This yellow star is
like our Sun -a G-
type star, with a
temperature of
about 6,00FC
(10,80FF).

This orange star
is a K-type star,
1 with a

temperature of
about 4,700 P C
(8,46FF).

Hot, blue stars Surface temperature Cool, red stars

The graph is called a Hertzsprung-Russell diagram, after
two astronomers, Enjar Hertzsprung from Denmark and
Henry Norris Russell from America, who made it in 1913.

This tiny star is a red
dwarf. It is a dim and
fairly cool star. It is ]
classified as an M-type,
with a temperature of
about 3,00FC (5,40FF).

Brighter Dimmer
. star star

cfcoAB

- *-

Absolute

magnitude

At this point, the binary
system would appear dim
from Earth because the
dimmer star is blocking
the brighter one.

From Earth, this binary
system would appear
bright, because the
brighter star is in front
of the dimmer star.

ECLIPSING BINARIES

About half the stars in the Universe belong to a double or
binary system in which two stars orbit about each other.
The two stars can be close enough to almost touch or
they can be millions of kilometres apart. We can detect
binary systems in different ways. If we have a side-on view
of a binary system from Earth, we can detect the changes
in brightness as the two stars take it in turns to pass in
front of each other. Theyare called eclipsing binaries.

VARIABLE STARS

Some stars vary in brightness. There are
different types of these variable stars. Some,
called RR Lyrae stars, change in less than a
day. Others, called Cepheid stars, take one to
100 days to change. Still more, called Mira
variables, can take up to two years to complete
one cycle of change. Cepheid stars change in
brightness because they change physically in
size and temperature. They give off more light
when they are expanding, and less when they
are contracting. The star won’t always be like
this - it is just a normal star going through an
unstable period in its life.

This diagram shows
how the brightness
of a Cepheid star
varies with time.

Find out more

Nuclear energy p.136
Sources of light p.193
Refraction p.196
Galaxies p.276
Life cycle of stars p.280
Sun p.284
Factfinder p.418

279

SPACE

Life cycle of stars

Nothing in the universe stays the same forever, and stars are
no exception. However, we cannot see a star changing because it lives
for billions and billions of years. The birthplaces of all stars are clouds
of gas and dust that have slowly formed from the sparsely scattered
atoms in space. Stars are born in groups, most of which break up, but
others are kept together by gravity. The rest of a star’s life depends
on how massive it is. The more massive a star, the quicker it uses
its hydrogen fuel, and the shorter and stormier its life is. Some
are simply so massive they explode. But most, like our Sun,
have a stable period in their lives when they shine steadily.

Nebula

New stars are
born all the time from
clouds of gas and dust.

Parts of the cloud collapse
under gravity. Each becomes
most dense at the centre, where
heat is trapped, to form a protostar.

When the protostar is hot enough,
nuclear fusion reactions start and energy
is released. It is now called a T. Tauri type
star. The rest of the cloud is blown away.

Stages in a star’s life

The Sun started its life in a group of stars, but now
it is on its own. The pictures here represent its life
cycle from a young star called a protostar, through
its present life as a stable, shining star, to its future
death as a white dwarf. Stars more massive than
the Sun are hotter and use up their fuel much
more rapidly, so they only spend a
fraction of their lives as a
stable shining star.

• e ® 9 ® (

Gravity

pulls hydrogen
atoms in the Sun
towards the centre,
where they smash and fuse
to form helium and energy. The

®* 8 »«® 9 8 » 9 , pressure at the centre keeps the

* ©* * o 0 V 0 ® star expanded. This is a stable period in

the star’s life. It is known as a main sequence star.

Open clusters
0 of young stars •

Clusters of
° middle-aged stars

9 Globular clusters
* of old stars

STAR CLUSTERS

Within the Milky Way Galaxy are concentrated
• groups of stars called star clusters. All the stars in a
cluster were born from the same cloud, are the same age,
and initially had the same composition. There are two
types of cluster - open and globular. Open clusters
contain up to a few hundred randomly arranged stars.
They are found in the outer parts (the flat disc) of our
Galaxy. Globular clusters contain hundreds of thousands
of very old stars arranged in ball shapes. They are found in
a huge sphere around the centre of our Galaxy.

OPEN CLUSTER
The Pleiades is
an open cluster
of young stars
that spreads
across 30 light
years in space
(in star terms,

“young” means
around 60 million
years old). To the naked
eye, the Pleiades looks like a
fuzzy patch of light with seven
prominent stars. Through powerful
telescopes, we can see many more of
its bluish stars, as well as gas and dust

that the stars have ploughed into.

A star like the Sun spends
10,000,000,000 years as a main
sequence star. The Sun is now in
the middle of its main sequence life.

The star’s luminosity
(amount of light it gives
out) increases as its
core becomes denser
and hotter.

Pleiades
cluster of stars

47 Tucanae
cluster of
stars

GLOBULAR CLUSTER

Globular clusters contain very
old stars. It is thought
they were f ormed
around the same time
as the galaxies that
they live in. This is
why globular
clusters can
provide infor¬
mation on the
early life of the
Milky Way. This
globular cluster, 47
Tucanae, is visible to
‘ naked eye if you live
the Southern Hemisphere.

280

SPACE

NEUTRON STARS

When a star several times heavier than the
Sun dies, its core collapses to become a
tiny neutron star, with a mass between
1.4 and 3 times the Sun’s mass. The
collapse is so violent that the electrons
and protons within atoms are forced
together to form neutrons. All the
material is squashed into an incredibly
dense sphere around 10 km (6 miles)
across. A pulsar is a fast-spinning
neutron star that flashes a signal
Earthwards as it spins (like a
lighthouse). Pulsars were first detected
1967 by British astronomers Jocelyn
►ell and Antony Hewish.

In 1054, the Chinese recorded a star bright
enough to be seen in daylight. It was a
supernova. Today, we see its remains in the
Crab Nebula. The core of the exploding star is
now a pulsar, rotating 30 times every second.

Red giant
star

The outer layers of the star become unstable
and puff away into space as a cosmic smoke
ring called a planetary nebula. The inner
layers do not have enough energy to keep
them expanded, and they collapse to form a
very small and dense white dwarf. This will
slowly fade to become a black dwarl.

Alternative deaths

Not all stars end their lives as white
dwarfs. Massive stars end their lives
in spectacular fashion - they
collapse so quickly that they
explode. This explosion is called a
supernova. The core may remain as
a neutron star or a black hole. The
star’s far-flung ashes will provide
material for new stars to be born.

gttgB

z mSm

■
. mbps

The hydrogen is used up. The
centre is so hot by now that the
star expands. The surface
cools and turns red. Such a
star is called a red giant.

The

helium left
begins to
fuse with
itself to
form
carbon.

The star
is now
called a
Cepheid,
it

continually
shrinks and
expands, losing
its outer layers of
material.

From Earth,

a supernova

looks like a

bright new star in

the sky - hence its

name (nova means “new").

The enormous gravity of a
black hole can drag in material
from a nearby star. This is
how a black hole is
discovered. As the
material swirls into
the black hole, it
becomes very hot
and gives off X-
rays. These X-rays
can be detected.

GENERAL RELATIVITY

In 1915, Albert Einstein published his
startling but now famous theory called
General Relativity. It gave a totally
different view of gravity, proposing that
it was a property of space, and not a
force between bodies. Bodies of matter
curve space, rather like a weight curves
a trampoline, and so bodies “fall”
towards other bodies. Even light
“falls” into the curved space around
a body and so its path is bent. This
strange idea was put to the test
during an eclipse of the Sun in 1919.
The light from a distant star was indeed
seen to be bent by the gravity of the
Sun. Einstein was proved right.

The star appears to be in a
different position from
where it actually is because
its light is bent by the Sun.

Around a black hole,
light is bent so much
that it cannot escape.

Actual
position
of star,.

Apparent
position
.of star

BIACK HOLES
Strange things happen to the
most massive stars at the end of
their lives. If the core has a
mass of more than three
times the mass of the
Sun, it will collapse,
becoming more and
more compact until
the star becomes so
dense that nothing, not
even light, can escape from its
gravity. It has become a black
hole, with a singularity (a point
of infinite density) at its centre.

According to General Relativity, bodies
of matter curve space. If the body of
matter is very dense (a large amount of
matter squashed into a small space), it
would stretch space into an infinitely
deep chasm - a black hole.

Find out more

Atomic structure p.24
Gravity p.1 22
Nuclear energy p.136
Origin of the universe p.275
Gaiaxies p.276
Stars p.278
Sun p.284

281

SPACE

Constellations

STAR TRAILS

From Earth, the stars appear to
spin around two imaginary
points in the sky - the north and
south celestial poles. This
photograph has captured the
movements of the stars as trails
in the night sky.

Earth inside
the “celestial
sphere”

From Earth, the
Sun appears to
move against
a background
of stars. The
star groups
it moves in
front of are
known
as the
Zodiac.

Star
patterns can
be used to
navigate
(Polaris, the
North Star, lies
above Earth’s
North Pole) or as a
calendar (from Earth
we see different star
patterns over the year as
the Earth orbits the Sun).

Some of the early star maps
were more artistic than scientific.

ORION

Orion, the hunter, is an easy constellation to
see. Four bright stars mark his shoulders and
knees. Three more mark his belt, and one
other, the Orion Nebula, marks his sword.

Grouping stars

An internationally agreed system
of 88 constellations is used by
astronomers today. Twelve of the
constellations are together known
as the zodiac. These form the
backdrop against which the
planets, the Moon, and the Sun
move. Individual stars are
identified within a constellation
by a letter of the Greek alphabet.
The brightest star is alpha, the
next is beta, and so on.

The TWINKLING PINPOINTS of light in the
night sky can all look the same at first. Thousands
of years ago, early astronomers divided the stars
into groups and drew imaginary pictures around
them so they were easy to remember - pictures
such as a scorpion or a bear. This is how our
present-day system of constellations was born. The
stars in a constellation are actually unrelated; they
only appear to make these groups when viewed
from Earth. The stars are all so far away that they
appear to be at the same distance and to move
together as if stuck on the inside of an enormous
bowl - the celestial sphere.

Modern
star map

STAR MAPS

Early star maps filled the northern sky
with animals and mythical figures. As
navigators voyaged south, more and more of
the sky could be charted. Positions of the stars
were pinpointed with increasing accuracy as
the telescope and observing techniques
improved; fewer charts with artistic
representations of the constellations were
produced. Celestial charts started to be made
photographically and then with the aid of
computers. Today, satellites plot positions of
the stars with even greater accuracy and speed.

Find out more

Life

Stui

Tele

Universe p.274
Stars p.278

’ CYCLE OF STARS P,

)Y OF ASTRONOMY I

SCOPES ON EARTH

Fact finder p.41 8

,280

>.296

p.297

MAGNITUDES
Astronomers use numbers to
describe a star’s brightness. The
scale of apparent
magnitude is so
called because it
doesn’t describe how
bright the star
actually is, just how
bright it is as seen
from Earth. The
larger the number
given to the star, the
fainter the star is.
Stars classified 1-6
are visible with the
naked eye.

282

SPACE

Orbit of Pluto

Orbit of
Uranus

Orbit of Mars

Orbit of Earth

Asteroid

belt

Orbit of
Jupiter

Orbit of
Saturn _

Orbit of Mercury

Orbit of Venus

Find out more

Gravity p. 122
Sun p.284

Mercury and venus p.286
Earth p.287
Mars p.289
Jupiter p.290
Saturn p.291
Uranus p.292
Neptune and pluto p.293
Factfinder p.418

Solar system

MILLIONS OF YEARS AGO, a family was born around the
Sun: balls of matter that we call the planets. The Sun and this
system of planets that orbit (circle) around it make up the
Solar System. Asteroids (minor planets between Mars and
Jupiter), comets, moons (bodies that orbit around
planets), and interplanetary dust also form part of
this large family which extends over 12,000 million km
(7,400 million miles) in space. The dominant body is
the Sun which accounts for more than 99 per cent of the
mass of the Solar System. Our Solar System was
once regarded as the largest and central
part of the Universe. Today, we know
it is just a tiny speck compared with
the rest of the Universe.

Astronomers have found discs
of gas and dust around some
young stars, where other
planetary systems
may be forming.

Orbit of
Neptune

Formation

The planets and other bodies
were formed 4,600 million years ago from
material left over from the Sun’s birth. The
Sun was surrounded by a rotating
disc of gas (hydrogen and
helium) and dust (iron,
rock, and snow) called
the solar nebula. The
dust came together to
form planetesimals (rocks
hundreds of kilometres
across), which then joined to
create four planets - Mercury, Venus,
Earth, and Mars. Farther out, dust and snow
combined with the gases to produce Jupiter,
Saturn, Uranus, and Neptune.

Pluto is a left-over
planetesimal.

All but two
planets, Mercury and Pluto,
have orbits in the same plane.

ORBITS

The Solar System is disc-like in
shape. The Sun is at the centre
and the planets follow individual
paths called orbits around it. They
all travel in the same direction,
but move at different speeds and
take different times to
complete an orbit.

GRAVITY IN THE SOLAR SYSTEM
What keeps the Solar System together? A
force called gravity, which is an attraction
between any two bodies that have mass.

Its strength depends on how massive
the bodies are and how far apart they
are. Gravity keeps the material in a
body together; if it is strong enough,
it will pull gases towards a planet or
moon to form an atmosphere. In the
17th century, the English scientist
Isaac Newton investigated the motion
of the Moon and the planets, and
outlined a universal law of gravitation. It

is one of the fundamental laws by
which the Universe operates.

Gravity keeps the planets orbiting
the Sun, and the moons orbiting
the planets. The effect of gravity
decreases with distance; the
farther a planet is from the Sun,
the slower it moves.

Mercury

Venus

Earth

• Mars

PLANET SIZES

Astronomers are more interested in the mass of
a body (the amount of material it contains)
than its diameter (its size). Of all the
planets, Jupiter has the largest mass as
well as the biggest diameter.

* Pluto

Saturn

Uranus

Neptune

283

SPACE

Sun

Prominences
are only
visible
during a
total solar
eclipse or
by using
special
equipment.

XHE NEAREST STAR TO US is the Sun. By studying it, we
can learn about the other stars in the Universe. Like all stars,
the Sun is a huge, luminous ball of hot gas - mostly hydrogen,
but some helium, with tiny amounts of other elements. Within
the Sun, a process called nuclear fusion continuously generates
energy such as light and heat; at its centre, the temperature is
around 14,000,000°C (25,000,000°F). The Sun was born from
a cloud of gas and dust about 5,000 million years ago. It was
created in a group of stars which slowly broke up so that now
the Sun is alone. It is the only star known to have a system of
planets. But to one of these planets, the Earth, the Sun is not
just any old star; it is a provider of energy for life.

Layers of sun

The Sun is made of different layers
of gas. The surface layer we see
is called the photosphere.

Here, gas swirls and
bubbles about, giving the
Sun a mottled look.

Surrounding the
photosphere is an
unseen layer of gas
called the
chromosphere.

Above this is a layer
of gas called the
corona (which
means “crown”).

Different parts of the
Sun take different
times to rotate. Its
middle takes around 25
days, while its top and
bottom take around 30. This
was discovered by observing
the movement of sunspots.

This ultraviolet picture of the Sun
reveals a hole in the corona.

Year 1 Year 4 Year 7 Year 10 Year 12

Sunspots go through a cycle lasting 11 years. At the beginning, the Sun is free of
spots. A few then appear high and low on the Sun’s surface. These then disappear
and new ones form nearer and nearer towards the Equator (middle).

PROMINENCES
Huge, flame-like clouds of hot gas sometimes
explode from the photosphere. These are
called solar flares and prominences,
and they are associated with
sunspots. Flares are short-lived
bursts of light. A large
prominence may reach heights
of 100,000 km (62,000 miles)
and may last for months.

NEVER
look at the
Sun directly
with your eyes,
through binoculars, or
through a telescope.

ULTRAVIOLET SUN
Today it is not only the visible light
given out by the Sun that can be
recorded. Astronomers have special
equipment that can take photographs
at other wavelengths,
such as ultraviolet or
infrared. These show up
details that normal
photographs cannot reveal.

SOLAR TELESCOPE

Astronomers use special instruments based on
Earth, and others up in space, to study the
Sun. The Sun’s light is collected and then an
instrument called a spectroscope is used to
split it into its spectrum (the different
wavelengths of light it emits).

Astronomers have gained most
of their knowledge about
the Sun by studying
its spectrum.

Sun’s light is
reflected down to a
mirror in an
underground tunnel.
The Sun’s image is
formed in an observation
room where astronomers
can study its light.

SUNSPOTS
On close inspection, the
Sun’s photosphere is at times riddled
with dark patches. These are sunspots -
patches of gas that look darker because
they are cooler. Sunspots are caused by
magnetic fields that slow down the flow
of heat from the Sun’s centre. They
have a dark central region called the
umbra, surrounded by a lighter region
called a penumbra. They generally
occur in pairs or groups.

One solar telescope
is at the Kitt Peak National
Observatory in the U.S.A.

Group of sunspots

284

SPACE

Venus

Mercury.

Find out more

Optical instruments p.198
Shadows p.201
Stars p.278

Life cycle of stars p.280
Solar system p.283
Fact finder p.418

Life of the sun

In star terms, our Sun is middle-
aged and will die one day. But
don’t worry; it has another 5,000
million years of shining to do
until it uses up its hydrogen
fuel. It will then start using its
helium; as it does so, it will
turn into a red giant star,
shining 1,000 times brighter
than now, and it will be
around 100 times larger in
size. Next, it will shrink to
become a white dwarf star,
the size of the Earth.
Thousands of millions of
years later, it will cool down
and end its life as a cold dark
body called a black dwarf.

SOLAR ECLIPSE

Occasionally, the Earth, Moon, and Sun happen to line up so that the Moon blocks
the Sun’s light from Earth. This is called a solar eclipse.The Moon’s shadow or
umbra only covers a small area of Earth’s surface. Anyone standing in this umbra
sees the Sun totally eclipsed by the Moon. Surrounding the umbra is an area of
partial shadow called the penumbra. From this area, the Sun is partially eclipsed.

ARTHUR EDDINGTON

The English astronomer
Sir Arthur Eddington
(1882-1944) was the
first to work out what
the inside of a star was
like. He discovered that
the luminosity of a star
(amount of light it gives
out) depends on how
massive it is. In 1919, he was
the first person to find proof of
Einstein’s theory of relativity;
during a total solar eclipse, he
recorded the displacement
(bending) oflightfroma
distant star.

This enormous orange-red sphere
represents the size that our Sun is expected
to grow to in its later life, when it has become
a red giant star. It will engulf the planet
Mercury, and probably Venus too.

After a calm passage
over the Sun’s equator, Ulysses ^
encountered a strong solar wind
_ from the other pole.

. This green band
represents the very
small area in our
Solar System where
sustainable life could
exist. Luckily for us,
one planet - the
Earth - formed
within this band.

T he Ulysses probe was launched in
1990 to investigate the poles of the
Sun (which are invisible from Earth).

Earth is in a

very fortunate

position in relation to

the Sun. Any nearer, and it

would have been too hot for the

evolution of life. Any farther away,

and it would have been too cold.

Light

from

Sun

A solar eclipse only occurs
when the Moon lies directly

Eclipses occur
because the Sun and
the Moon appear to
sizeifT
In fact,
400 times
it

appears Moon-sized.

Path of the
Ulysses probe

SOLAR MAX AND ULYSSES
Scientists are interested in
knowing the total amount of
energy received every second from
the Sun at the top of the Earth’s
atmosphere. This is called the solar
constant. Changes in this can affect
Earth. A satellite called Solar Max
investigated the solar constant in the
1980s. A space probe called Ulysses
investigated the Sun further in 1994-5.

Mars

The Ulysses probe
used the gravity of
the planet Jupiter
to swing into the
correct path.

At this point, Ulysses
was buffeted by a
fast “wind” of hot gas
streaming from the 1
Sun’s pole.

285

SPACE

Mercury

Venus

Metallic

Rocky mantle

core

MERCURY STRUCTURE
The weak magnetic field and high
density of Mercury point to an
enormous iron core. Above this is
a layer of compressed molten
rocks - the mantle. A solid, rocky
crust floats on top of the mantle.

Mercury

A spacecraft, Mariner 10,
gave us most of our
information about
Mercury’s surface. Only
part of the planet was
mapped because Mariner
always flew by on the same side.

There is plenty of Mercury still to be explored.

MERCURY CRATERS
Like our Moon, Mercury is
small and scarred by craters
that were formed soon after
the birth of the Solar System.
It also has cliffs, or scarps,
which formed when the
young, cooling Mercury
shrunk like a shrivelling
apple, wrinkling its surface.

Mercury and venus

THE CLOSEST PLANETS to the Sun, Mercury and
Venus were known and observed even by early
people. Mercury is the most difficult to see because
the Sun’s glare usually blinds us to it. By contrast,
Venus is easy to see. It is the brightest object in the
sky after the Sun and the Moon. Like the Moon, it
goes through a cycle of phases, from a slim crescent
to a full disc. Galileo Galilei was the first person to
observe this cycle in 1610. But it was only this
century, when probes were sent into space for the
first time, that astronomers built up
our present-day picture of barren
and lifeless Mercury, and of the
hostile world that lies behind
Venus’ serene face.

Crust

Mantle

Core

FORMING CRATERS
The many craters on Mercury’s
surface were formed when rocks
smashed into the planet. The
material blasted away from the
surface left saucer-shaped hollows.

MERCURY LANDSCAPE
The surface gravity of
Mercury is under half
that of Earth. This is
too weak to hold gas
to the planet and so
Mercury has almost
no atmosphere.

Without air, sound
cannot travel, and so it
is also a silent world.
Without an atmosphere
to keep in heat, Mercury
has the biggest day and
night temperature variations
of any of the planets: burning
hot days of 400°C (752°F), and
freezing cold nights of -200°C (-328°F).

VENUS STRUCTURE
Like Earth, Venus underwent
a molten period when denser
material sank to the centre,
leaving a lighter crust. Its
molten iron-nickel core is
surrounded by a rock mantle
which supports the rock crust.

Venus

Venus is completely choked by
a thick, dense atmosphere.
Upper cloud layers rotate
every four days - much
faster than the 243
days it takes the
rocky planet to
complete one
rotation about its
axis. It is the Sun’s
reflection on these
heavy clouds that we
see from Earth.

SURFACE IMAGE
Over 20 spacecraft have
investigated Venus. They have
revealed a surface of hot desert
with a small amount of lowland
and highland.

VENUS LANDSCAPE
Anyone thinking of
landing on Venus
has to travel
through its
atmosphere
first. This
consists of thick,
yellow-white clouds of
sulphuric acid gas. On
the surface, the heat is
an intense 480°C
(895°F) because the
atmosphere works like a
greenhouse, trapping the
Sun’s energy. Finally, the
surface pressure, 100 times
that of Earth, would crush
any human in seconds.

Image of Venus’ surface taken
by Magellan space probe

Find out more

Solar s\stem p.283
Sun p.284
Earth p.287
Moon p.288
Space probes p.301
Factfinder p.418

286

SPACE

Earth

Crust Mantle

Outer

core

Inner

core

EARTH STRUCTURE
The young Earth was formed with
the other Solar System planets 4,600
million years ago. At first it was cold,
but radioactivity heated it until it
melted. The heavy iron sank to the
centre and the lighter rocks floated
to the top. Today, Earth’s iron core
is surrounded by a fluid mantle of
rock. The rocky surface crust we live
on is only a few miles thick.

J #

WHAT IS THE MOST thoroughly investigated planet in the Solar
System? Earth, of course - more is known about it than about any other
planet. Like all the others, it is unique. It has features that are not found
anywhere else in the Solar System. An obvious one is that it is the only
planet supporting life. But the presence of water is equally unique. These
two factors shaped its evolution from a molten planet with a hydrogen-
rich atmosphere to today’s world. Life started in Earth’s oceans 3,000
million years ago. The development of life forms helped produce today’s
atmosphere of nitrogen and oxygen which in turn helps provide the
conditions to maintain life. Earth is the third nearest planet to the Sun.

It has one natural satellite - the Moon.

ACTIVE EARTH

The surface of Earth is constantly changing. Its crust is made of enormous
moving slabs or plates. Volcanoes and earthquakes occur as these plates
collide and rub together or slip beneath
each other. Molten rock forces
its way to the surface. In
this way, the

Planet earth

Earth shines brightly in space. It
reflects about one-third of the
sunlight that falls on it. Earth’s
atmosphere scatters the light
and creates a predominantly
blue-coloured planet. Brown
land masses are visible, as are
the oceans that cover around
two-thirds of the Earth’s
surface. The Pacific Ocean
alone covers half the globe.

Many clouds can be seen
in the atmosphere.

ARISTARCHUS

The fact that
Earth travels
around the
Sun has been
accepted for
less than 400 years. Copernicus,
the 16th-century Polish
astronomer, is usually credited
with disproving that the
Universe is Earth-centred. But a
Greek astronomer, Aristarchus,
(310-230 B.C.) working centuries
earlier, had the idea first. Using
geometry, he worked out the
relative sizes and distances of
the Sun and Moon. He
concluded that as the Sun is by
far the largest, the Earth must
travel around the Sun.

Earth’s crust
renews
itself.

EARTH ATMOSPHERE
Compared to its neighbour Venus, Earth has
a thin atmosphere - thin, but very useful. It is
thin enough to let sunlight through, but thick
enough to bar the way of other forms of harmful
radiation from the Sun; ultraviolet rays, dangerous
to human life, are mostly filtered out. The
atmosphere also slows down and vaporizes tiny
space rocks known as meteoroids. It also
provides the air we breathe.

The conditions on
Earth are just right for
life forms such as us!

EARTH IANDSCAPE
Millions of years ago, an
; atmosphere of carbon dioxide,
water vapour, and nitrogen formed
around Earth. The water vapour
formed rain which made the oceans.
Today, both of these features are very
important. Water is exchanged
between the atmosphere and the
oceans, while the atmosphere acts like a
blanket to keep an almost even temperature.

Find out more

Formation of
THE EARTH P.210
Structure of

THE EARTH P.212
Solar system p.283
Fa ct finder p . 418

287

SPACE

MOON

Astheno-

sphere

Core

MOON STRUCTURE
Scientists have discovered that the
Moon has a small iron and sulphur
core surrounded by a layer of partially
melted rock (the asthenosphere).
Above this is a layer of solid rock (the
lithosphere), covered by a crust of
calcium and aluminium-rich rocks.

The NEXT-DOOR NEIGHBOUR of Earth in
space is the Moon - a ball of rock that spins on
its own axis as well as orbiting the Earth and
travelling with the Earth as it orbits the Sun. It
is one of the best studied objects in the Solar
System. Detailed maps of the side that faces
Earth were drawn soon after the invention of
the telescope. In the 1960s, space probes were
sent crashing into its surface, and orbiting
around it. In 1969, people even walked on the
Moon, and brought back rocks from its
surface. All the Solar System planets except
Mercury and Venus have moons. They range a
great deal in size, but Earth’s moon is one of
the largest - around one-q'uarter of
the size of Earth.

v BIG SPLASH
Astronomers
cannot say for certain
where the Moon
came from. It may
have broken off
from Earth, been
captured by Earth, or
formed from material
around the young
Earth. A fourth idea, the
big splash theory, is that a Mars¬
sized body collided with the
young Earth. Debris from this
collision formed the Moon.

The surface of the Moon
has changed little for
millions of years;
with no atmosphere
there is no
weathering effect.

LUNAR LANDINGS
The seventeen Apollo missions of the
1960s and 1970s are still regarded as
the high point of space exploration.
These missions set twelve astronauts on
the Moon and returned them safely
back to Earth. The results from surface
experiments, orbital flights, and many
photographs are used to produce our
picture of the Moon’s surface.

Crescent

Moon

Gibbous Moon. The
Moon has started to
wane (“shrink") in
Earth’s sky.

Sunlight

Nobody would
hear you shout
on the Moon!

Earth

Moon watching

The Moon is a good object for
novice astronomers to
observe because its surface
features are easily visible to
the naked eye. The dark
patches that can be seen are
flat areas of land called
maria”. The lighter areas are
mountains. Binoculars can even
reveal some of the craters that
cover much of the Moon’s surface.

Full Moon. The
Moon is behind
Earth (but not in
Earth’s shadow). We
see the whole of the
Moon’s sunlit face.

New Moon. The Moon lies
between the Sun and
Earth. The side facing
Earth is in darkness.

Crescent Moon.
The Moon has
started to wax
(“grow") in Earth’s sky.

Gibbous Moon. The
Sun lights up most
of the side of the
Moon that faces Earth.

MOON ROCK
Around 2,000 samples of moon
rock, weighing almost 400 kg
(880 lb), have been brought
back to Earth. By studying these
rocks, scientists have built up a
picture of the composition and
history of the Moon. Some
rocks, for example, were
formed from molten lava.

MOON LANDSCAPE
If you landed on the Moon, you would
find a very quiet world. It has no
atmosphere surrounding it and so sound
cannot travel (and you wouldn’t be able to
breathe either!). Craters up to hundreds
of kilometres wide cover its surface. Many
of them were formed around 4,000
million years ago when rocks from the
asteroid belt collided with the Moon.

PHASES OF THE MOON
Even though it has no light of its own, the Moon is the
brightest object in the night sky because it reflects
sunlight well. As the Moon travels around Earth we see
different amounts of its sunlit face - ranging from a thin
crescent to a full face. When the side of the Moon facing
us has no sunlight on it, we cannot see it at all. We call
this a New Moon. The lunar month, which lasts 29.5
days, is measured from one New Moon to the next.

Find out more

Waves, tides, and
CURRENTS P.235
)OI AR SYSTEM P.28;

Earth p.287
JMANS IN SPACE P.3
Factfinder p.418

288

SPACE

Drawing of Mars
by Percival
ln^ Lowell

The brightest red “star” in Earth’s sky is

actually the planet Mars. This red colour, the most
distinctive feature of Mars, comes from rock and dust
covering its surface. When two Viking spacecraft
landed on Mars in the summer of 1976, they analysed
the soil and found it to be iron-rich; Mars is just rusty!
Spacecraft have revealed several gigantic volcanoes and
a set of canyons, called the Valles Marineris - this is ten
times longer and four times deeper than the Grand
Canyon in the United States. There are also dried-up
river beds, showing Mars was warmer and wetter long
ago. Simple life may have started then. The
Viking landers searched unsuccessfully for life
but some scientists believe they have found
fossils of Martian cells in a meteorite.

Mantle

Lowell
observed Mars
and interpreted surface
markings as water-carrying
canals built by an advanced
Martian civilization.

MARS STRUCTURE
The young Mars was only fully
molten for a short time. This
meant that some of the heavier
material was prevented from
sinking to the centre. This
made Mars’s core smaller than
those of the other rock planets.

PERCIVAL LOWELL

Percival Lowell
(1855-1916), a

rich amateur 1 1H '

astronomer, it I Jffm

was fascinated
by Mars. .:3 k

Looking at it H

from his BggKH

observatory in
Arizona, U.S.A., ‘flSnrfc
he believed he HppjuJ
could see canals on
the planet. He though
it was inhabited and the canals
took water from the polar caps
to dry farmland. They turned
out to be an optical illusion.

The planet’s deep red
colour led to its
SW being named
mm after the God
of War,
Bk Mars.

Rugged planet

The surface of Mars is covered with
dramatic features such as deserts, A
high mountains, deep craters, dm
and enormous volcanoes. Mars jfi|
also has two polar ice caps Sk
that change with the J9
Martian seasons - the JH
carbon dioxide ice melts in

summer, uncovering a H
surface of layered rocks, I
and forms again in winter. B

PHOBOS
Two tiny moons,
Deimos and Phobos,
vlHfc orbit around Mars.
•>. • y From Earth, they

l°°k like specks of
light, even through
our most powerf ul
telescopes. Spacecraft
have shown they are dark, strangely
shaped bodies. Both have craters, but
Phobos is also covered in grooves. In
many ways, the moons of Mars are
like asteroids - some scientists
HL think they are members of the
asteroid belt that have been
captured by Mars.

Phobos
(meaning
“terror") was i
named after I
a mythical ’1
servant of the
God Mars.

R mars

LANDSCAPE

If you were transported to Mars,
you would Find a lonely and cold
place. Its gravity is about half as
strong as Earth’s and so the planet
in only hold on to a thin atmosphere,
m so, at certain times wind speeds
ase to over 100 km/h (62 mph),
o upa dusty storm that lasts for j
months. The dust makes the sky appear pink. t!

MARTIAN BACTERIA?
This meteorite, which fell in
Antarctica, almost certainly came
from Mars. In 1996, American
scientists found that it contains
many tiny worm-shaped structures,
each one-thousandth the thickness
of a human hair. These may be the
fossils of early Martian cells,
similar to bacteria on Earth.

Robots p.176
Volcanoes p.216
Solar system p.283
Earth p.287
Moon p.288
Asteroids p.294
Fact finder p At S

OLYMPUS MONS
The giant volcano Olympus Mons is not
only the largest mountain on Mars, but
in the whole Solar System. At 700 km
(435 miles) across and 27 km (17 miles)
high, it is around three times as high as
Mount Everest on Earth.

289

SPACE

Jupiter

Liquid hydrogen

J J

JUPITER STRUCTURE
Jupiter’s small, rocky core is
surrounded by an ocean of hydrogen
in metallic and liquid form. Above
this is the vast atmosphere of
hydrogen and helium, eight times
thicker than Earth’s. The
temperature drops
towards the cloud
tops; the core is at
35,000°C
(63,000°F), while
the upper cloud
layers are at
-140°C (-220°F).

JUPITER
ATMOSPHERE
If you were
landing on
Jupiter, you
wouldn’t “land”
at all but would
sink through its
atmosphere - a
1,280 km-(795 mile-)
thick layer that
contains methane and
ammonia, as well as
hydrogen and helium.
The Galileo probe found
less water than expected,
and very strong winds
deep in the atmosphere.

JUPITER

Metallic hydrogen. At
very high pressures,
hydrogen behaves
like a metal.

Core

GALILEO
GALILEI

The Italian
astronomer and
physicist Galileo
(1564-1642)
discovered four
of Jupiter’s
moons in 1610; Io,
Europa, Ganymede,
and Callisto are known as the
Galilean moons. Galileo used
the discovery to try to convince
people the Earth was not the
centre of the Universe, but
that the Earth and planets
move around the Sun.

& •

The GIANT PLANET in the Solar System is Jupiter - it contains
three times more mass than the other eight planets put together.
It is mostly made of gases and liquids, with a fairly small rocky
core. The thick clouds at the top of its atmosphere reflect
sunlight well and so the planet shines brightly in Earth’s
night sky. Much of our knowledge of Jupiter has been
learnt through space probe missions. Four craft flew by
in the 1970s, and now the Galileo space probe
is orbiting around it. This is making long-
The Galileo spacecraft term observations of Jupiter, its moons,

Jupiter's atmosphere in and its strong magnetic field, which IS

December 1996. a detachable around 4,000 times greater than Earth’s.

heatshield saved it from
burning up; then a parachute
took over. The main Galileo
spacecraft went into orbit
around Jupiter.

Hydrogen, helium,
and ammonia ice
crystals form the
clouds in the
upper layers
of the

atmosphere.

COMET IMPACT

In 1993, American astronomers Gene
and Carolyn Shoemaker and David
Levy discovered a remarkable comet,
that looked like beads on a string.
Comet Shoemaker-Levy 9 had been
broken up by Jupiter’s powerful
gravity. The following year, the
comet fragments crashed into the
giant planet. The impacts created
huge hot spots, bigger than the
Earth, and long-lasting dark clouds.

Storms

Jupiter takes
just under ten
hours to rotate on its axis.
This fast spin causes high winds. As the
gases in the atmosphere circle the
lanet, they produce colourful belts and
zones in the cloud tops. Giant storms
are created. The Great Red Spot, more
than twice the size of Earth, is the biggest
hurricane in the Solar System.

Just a little bigger than Earth’s
Moon, Io is one of the most
remarkable bodies in the Solar
System. It is among the largest
of Jupiter’s family of 16 moons.
Jupiter’s strong tidal force

helps heat Io’s core, leading
to the formation of
active volcanoes.

Find out more

Atmosphere p.248

>OIAR SYSTEM P.28;

Moon p.288
>PACE PROBES P.301
Fact FiNBER p.418

290

SPACE

Saturn

Metallic

hydrogen

Liquid hydrogen

The PLANET that just looks like a bright star
from Earth has turned out to be the jewel of the
Solar System. Saturn is the sixth planet from the
Sun and is almost twice as far away as its neighbour
Jupiter. It is a gas giant and is well known for its
amazing system of coloured rings. Since 1610,
astronomers have gazed through telescopes at
Saturn. But explaining what they saw was a major
problem. The extent and complexity of the
Saturnian system was finally revealed by the
Voyager space probes in the early 1980s.

Atmosphere

SATURN STRUCTURE
There are three distinct layers inside Saturn. It
has a central rock-ice core which is surrounded
by metallic hydrogen. The outer layer is made
up of hydrogen and helium - liquid near the
centre but turning to a gas farther out.

EARLY OBSERVATIONS
When Galileo observ ed Saturn in 1610, he
saw three bodies. Was it possible that Saturn
was a triple planet? A few years later,
astronomers were surprised to find that
the two small globes had moved and A

changed shape. In 1659, Christiaan M

Huygens, a Dutch astronomer,
correctly explained that they were nj
observing Saturn’s rings whose
appearance changed as the
planet orbited the Sun.

RINGS

Jupiter, Saturn, Uranus, and
Neptune all have rings. But Saturn’s
are by far the most
spectacular. From Earth,
astronomers worked out
that the rings were not
yKSP^solid as they could see stars
through them. Spacecraft
have revealed that the
rings are made of
UppgSScountless pieces of icy rock
'■ “ some pieces are as small

as dust, others as big as
huge boulders. Saturn has
not always had rings. It is thought
they were created when orbiting
moons collided.

BULGING EQUATOR
Saturn spins very quickly on its
axis; its day is only 10.5 hours. /
Combined with the planet’s
low density, this creates Saturn’s 1
bulging equator. In fact, Saturn’s
tummy bulges more than any other
in the Solar Systtm^^^^

gpg Cloud bands

^ The coloured clouds on the
surface of Saturn’s atmosphere
form bands around the planet.
^ These clouds are made from
ammonia and other chemicals. Oval
spots can sometimes be seen in the
bands; these are storms. On a blustery

would stfSttk da y on Saturn, winds up
v ftoatj to 1,800 km/h (1,120

mph) can blow in jd
\ the upper air.

r. SATURN MOONS M nM

The prize for the planet with the A

most moons is won by Saturn. / .-.rN

Eleven were discovered from Earth IMfc...
and a further seven from spacecraft. ^Hh||

It is possible there are even more. The

first to be discovered was the largest

moon, Titan, in 1655. It is unique because it is

the only moon that has a heavy atmosphere covering its surface.

Ten of Saturn’s small moons are irregular, potato-shaped bodies.

FLOATING PLANET
Although Saturn has 95 times the mass
of the Earth, its average density is so low
that it is the only planet lighter than the
same volume of water. This means that
if we could put Saturn in an enormous
bucket of water, it would float.

Find out more

Floa

TING AND SINKING
>OLAR SYSTEM P.28:

Moon p.288
>PACE PROBES P.301

Factfinder p.418

p.129

291

SPACE

Uranus

ASTRONOMERS WERE DUMBSTRUCK by the discovery of Uranus
in 1781. Until then, it was thought that the Solar System consisted of
the planets as far out as Saturn but no more. Its discovery doubled the
size of the Solar System at a stroke - Uranus is twice as far from
the Sun as Saturn. At such a distance, little was learnt about
Uranus until a space probe called Voyager 2 flew by in 1986.
It found a cold gas giant with a system of 15 moons and at
least 11 thin, black rings surrounding it.

Blue-green planet

Even through Earth’s best telescopes,

Uranus appears as a fuzzy blue
green ball of gas; methane in its
atmosphere reflects blue and
green sunlight. Through the
cameras on Voyager 2,

Uranus still appears as a
featureless globe. But
computer processing
has revealed occasional
white clouds of
methane ice crystals,
carried around the
planet by winds.

Atmosphere

Water, ammonia,
and methane

Core

URANUS STRUCTURE
The rocky core of Uranus makes
up about one-quarter of the
planet’s mass. Above this is a
layer of water, ammonia,
and methane, in ice
and liquid f orm. The
outer layer is made
up of hydrogen and
helium gases.

URANUS
MOONS
Five of
Uranus’
fifteen
moons were
discovered
from Earth.

The ten
smaller ones
were revealed
by Voyager 2’s
cameras in 1986.

The farthest moon
is called Oberon - it
circles at 582,600 km
(361,795 miles)
out from Uranus.

Uranus' moons and rings
circle around the middle
of the globe.

URANUS LANDSCAPE
It doesn’t get any warmer
than -209°C (-344°F) on
Uranus. The planet
g receives about 370 times
less sunlight than Earth,
although its atmosphere
carries what heat there is
around the planet. If you found
yourself on Uranus, as well as being very cold,
you would sink into the choking atmosphere
of hydrogen, helium, and methane.

TITANIA

The moons of Uranus are
dark bodies of rock and
ice. Titania is the
largest. Craters and
valleys cover its surface.

SIDEWAYS
PLANET
Uranus appears
to lie on its side. It
is thought that the planet
was tipped up when the
last few huge chunks came
together to form it.

Page from C^-v,

Herschel’s diary ^

DISCOVERIES

1781 Uranus discovered

Cerman astronomer William Herschel
was not looking for a planet; but during
routine observations on 13 March he
found Uranus. This led astronomers to
believe other planets may lay
beyond undetected.

1846 Neptune discovered

Neptune’s position had been
calculated and a search was carried out.
Johann Galle from Germany located it
on 23 September 1846.

1930 Pluto discovered

The American Clyde Tombaugh found
Pluto when he was comparing
photographic plates in January 1930.

One of Uranus’ moons,
Miranda, is a hotch-potch
of deep craters, high
cliffs, and smooth plains.
Most are ancient
structures, but
surprisingly some have
been formed more
recently.

Find out more

Nkp'

>OLAR SYSTEM P.28;
Saturn p.291

TUNE AND PLUTO P
>PACE PROBES P.301

Factfinder p.418

.293

292

SPACE

Water,

ammonia, and
methane

Atmosphere

Neptune and pluto

Pluto

Core

NEPTUNE STRUCTURE
Neptune has a small rocky core,
surrounded by an ocean of
water, ammonia, and methane.
Its atmosphere is made of
hydrogen, helium, and
methane. The methane gives
Neptune its intense blue colour.

m i

The TWO MOST DISTANT PLANETS are worlds of
contrast. Neptune is the most distant gas giant. Pluto
is a frozen world, the smallest of all the planets. Their
existence was not known until fairly recently. Both
were predicted and then discovered within the last
150 years. The two planets are so distant that very
powerful telescopes are needed to see them. Details
of Neptune were revealed when Voyager 2 flew by in
1989. Its images showed that Neptune had a
thin, dim ring system. Pluto remains the only
planet that has never been investigated
by spacecraft.

Water-ice

Water and

methane

Core

Neptune

Voyager images of Neptune
show a blue planet, flecked
with white clouds of methane
ice crystals. A region known
as the Great Dark Spot in the ,
Southern Hemisphere is in
fact a huge storm
that rotates
around the
planet.

PLUTO STRUCTURE
The make-up of Pluto is very different from
that of the other outer planets. Its density
suggests that it has a rocky core. Its
methane frost surface probably
covers a water-ice layer below.

PLUTO

The unexplored planet Pluto is
the smallest in the Solar System.

It has one moon called Charon,
which is fairly close to Pluto, and
is about half its si/e. This makes
it difficult to separate the two
bodies when viewed from Earth.

PLUTO LANDSCAPE
If you were unlucky
enough to land on Pluto,
you would find a frozen,
lonely, and very dark
world. Because Pluto is
nearly forty times farther
from the Sun than the
Earth, the Sun would
probably just look like a
very bright star.

NEPTUNE IANDSCAPE
Being on Neptune
would be a very windy
experience. The Voyager
spacecraf t has recorded
winds of up to an
incredible 2160 km/h
(1340 mph).

Nereid, a
moon of
Neptune

Two of Neptune’s moons,
Triton and Nereid, were
discovered from
Earth. Six more
were discovered
by Voyager 2.

Pluto

Much about
such as its orbit,
leads astronomers to
question whether it is
a planet at all.

NEPTUNE MOONS
One of Neptune’s
eight moons, Triton,
has two very different
hemispheres. The
south pole has active
volcanoes and a pink
cap of nitrogen and
methane ice, while
the north pole is
r bluish with many
shallow valleys.

ND PLUTO

the discovery of Pluto in 1930,
scientists have thought there is a
X” whose gravity is pulling on Uranus
Neptune. But new measurements show no
such pull. Instead, astronomers have recently
found dozens of “ice dwarfs”
beyond Pluto, each a frozen
lump of ice about a
hundred kilometres
(60 miles) across.

In close-up, an ice dwarf would
probably look like Saturn’s moon
lapetus/Hyperion - a mix of bright ice
with dark rocks or organic compounds.

ORBITS

Pluto moves in strange ways. Its
orbit is tilted f urther and is more
elongated than that of any other
planet. In fact, for part of its orbit,
Pluto moves closer to the Sun than
Neptune, so that for a time,
Neptune is the most distant planet
in the Solar System.

Find out more

)OLAR SYSTEM P.28'
Uranus p.292
>PACE PROBES P.301

Fa ct finder p . 418

293

SPACE

If all the asteroids were put together,
they would still only make up a tiny
fraction of Earth's mass.

Asteroids

Did YOU KNOW that there are really millions of planets orbiting the Sun? Apart from
nine “proper” planets, there are a few million minor ones, called asteroids. These are
different-sized chunks of rock, ranging from specks of dust to some which are a
few hundred kilometres across. Most of them travel in an orbit between Mars
and Jupiter called the asteroid belt. Others follow different orbits. In the
18th century, astronomers were convinced that a missing world
existed between Mars and Jupiter. A search was mounted and
the first asteroid, Ceres, was found by chance in 1801.

Today, over 6,000 have been catalogued.

ASTEROID BEI.T
Although the main
planets formed from a
disc of material surrounding
the young Sun, the material in
the region of the asteroid belt did
not form a planet. It was prevented

from clumping together by the
enormous gravity of nearby Jupiter.

T he smallest asteroid seen so far from Earth is around
150 m (490 ft) across. Space probes travelling through
the belt have detected some only millimetres in diameter.

ELEANOR HELIN

American astronomer Eleanor
Helin has spent many years
discovering and charting asteroids,
particularly those that come close
to Earth. She works in California,
where she makes detailed studies
of photographic plates, searching
through the stars for new asteroids.
The relatively fast movement of an
asteroid against the
background of
distant stars is
captured on
photographic
plates
mounted on
special
telescopes.

Asteroid orbits

^ Most asteroids journey around the Sun in the asteroid belt.
Others are in smaller groups with different orbits. A
group named the Trojans travel along Jupiter’s path:
some in front of the planet, and some behind. A group
called the Apollo family have orbits that cross the path of
Earth. One remote asteroid called Chiron orbits between
Saturn and Uranus. At this distance from the Sun, it is
made of ice, not rock.

NAMING ASTEROIDS

New asteroids are numbered and
later named f rom suggestions that
can be made by their discoverers.

1801 The first asteroid is
discovered. It is numbered 1
and named Ceres.

1891 Asteroid number 323 is
the first to be discovered by
photography. It is named Brucia.

1977 Asteroid number 2060 is
discovered and named Chiron.

It has the mostdistant orbit
of an asteroid.

1983 Asteroid number 3200 is
the first to be discovered by a
spacecraft. It is named Phaethon.

FIRST PHOTOGRAPH
Until 1991, asteroids had mainly
been studied from Earth-based
telescopes. In October of that
year, the Galileo space probe,
on the way to Jupiter,
observed an asteroid called
Gaspra that lies on the
edge of the asteroid belt.

The probe took the first
close-up photographs of an
asteroid. Gaspra is a small,
irregular-shaped asteroid,

12 km (8 miles) across, which
rotates once every seven hours.

asteroids
are irregular
in shape.

ASTEROID SIZES
Astronomers can calculate an asteroid’s size
by studying its brightness (how much of
the Sun’s light it reflects), by timing
it as it crosses a background star, or
by direct measurement if it comes
close to Earth. The largest asteroid,
Ceres, is 933 km (580 miles) in
diameter, but most are under 100 km
(62 miles). Many would
dwarf the Empire State
Building (in the
United States).

Find out more

Com]

>OLAR SYSTEM P.28:
Mars p.289
Jupiter p.290
ETS AND METEORS
Ipace PROBES P.301

p.295

294

SPACE

Comets and meteors

HAIRY STARS

Comets have been observed and recorded for
thousands of years but they have not always
been understood. They were once called “hairy
stars” and their sudden appearances made
superstitious people regard them as bad omens.

EDMOND
HALLEY

The English
scientist Edmond
Halley (1656-1742)
worked in many
areas of
astronomical
research, but he is best
known for his work on
comets. He showed that comets
observed in 1531 and 1607, and one
he saw himself in 1682, were in fact
the same comet. He predicted that
it would return in late 1759. It did.
And again in 1835, 1910, and 1986.

It is known as Comet Halley. He was
the first to show that some comets
follow orbits that keep returning
them to the vicinity of the Sun.

Imagine A GIANT, DIRTY SNOWBALL streaking
around the very edge of the Solar System. This is
a comet. Beyond Pluto’s orbit are the leftovers
of the cloud that formed the Solar System. It
contains billions of icy lumps called comets,
and now and then, one may be knocked off
course and onto a path towards the Sun.

Here, the ice boils away to form an
enormous head and a long tail. As a
comet travels, it sheds bits of itself;
from Earth, these are seen as showers
of light called meteors. Astronomers would love
to get hold of a comet sample because it would be a
piece of evidence from the birth of the Solar System.

Comet
West on
13 March, 1976

Nucleus of a comet

People could only guess what a comet’s nucleus
was like until a space probe called Giotto flew
past the nucleus of Comet Halley in
1986. It sent back photographs
showing a nucleus that looks
like an icy, rocky potato and
measures 16 x 8 km
(10x5 miles). This was the
first confirmation that
comets are giant, dirty
snowballs (predicted
by an American,

Fred Whipple, in 1949).

As a comet travels
away from the Sun, its
tail gets smaller until
the comet is once
again just a dirty
snowball.

A comet’s tail always points aw ay from
the Sun. So if a comet is travelling away
from the Sun, it travels tail first.

Once a comet is near the Sun, the comet
starts to shed material. Comet Halley will
make around 2,300 more trips around the

For most of a comet's life, it is a dirty
snowball. When it travels close to the
Sun, the surface snow is turned to a head
of gas called a coma. The Sun’s
radiation sweeps this into a gas tail.

Dust particles are also swept back
to form a dust tail.

Dust tail

Gas tail

meteorites

Meteorites are any old lumps of
interplanetary rock (from asteroids or the
surface of planets, for example), large
enough to survive the journey through
Earth’s atmosphere. Most are fist-sized.
But larger ones have smashed into Earth.
The Barringer meteorite landed in
Arizona, United States, producing a
crater 1.3 km (0.8 miles) across.

Every August,
Earth travels
through a band of
dust which is
material from a
comet called
Swift-Tuttle. This
results in a meteor
shower called the
Perseids.

meteor shower

Comets shed enormous amounts of gas and dust.

After about 1,000 years, this dust forms a
ring. If the Earth passes through this,
the dust burns up in the atmosphere.
From Earth, this is seen as a meteor
shower or shooting stars.

Meteorite crater in
Arizona, U.S.A.

Find out more

)OLAR SYSTEM P.28'
Asteroids p.294
Factfinder p.418

295

SPACE

Study of astronomy

Change of direction

During the 19th century, the focus of
astronomy changed. Rather than
cataloguing and trying to understand the
movement of stars, astronomers thought
about what stars actually were (the
study of astrophysics). In the 1860s, a
British astronomer, William Huggins,
analysed the light from stars (their
spectra). Others took up this work,
and soon the stars were able to
be classified by their spectra.

JOHANNES
KEPLER

Danish astronomer
Tycho Brahe (1546-
1601) spent years
cataloguing the stars
and planets with
great accuracy. His
assistant Johannes
Kepler (1571-1630) put
his observations to good use.
He developed three important
laws of astronomy. His first law
describes the shapes of planetary
orbits. His second law describes
the speed at which the planets
travel along their orbits. His third
law relates the different planetary
orbits to one another.

Mayan observatory in
Mexico dating from
1 st century

ASTRONOMY IS THE oldest science. For thousands of years, people have
sought to understand space and Earth’s position in it. As long ago as 4000
B.C., the Egyptians developed a calendar, based on the movement of objects
in space. Observation of the skies continued, and soon events such as
eclipses could be predicted. Since the 17th century, the pace of discovery
and understanding has quickened. We have learnt more about space this
century than at any other time. Today, the astronomer is no longer a
person working in many fields of science, but is a specialist who
concentrates on one specific aspect of astronomical research.

ANCIENT ASTRONOMY
Ancient civilizations around the world relied
on the movements of the bodies in space.
The positions of the Sun and Moon were
used to measure time - in days, months,
seasons, and years. The Sun, Moon, and
stars were also used to navigate on land
and sea. As the bodies were not fully
understood, some astronomical
happenings were believed to be ill omens.

USING TECHNOLOGY
Early astronomers had to work with their eyes
alone. In the 16th century, Tycho Brahe made the
most accurate measurements of the stars possible
with the naked eye from his observatory. The
telescope was first used in the 17th century, and
over the years, it has remained the astronomer’s
fundamental tool. Today, powerful telescopes,
satellites, and space probes arc all used to collect
information from space. Scientists then use
sophisticated equipment to study the data.

PRESENT-DAY ASTRONOMY

As astronomers answer questions that puzzle them, new
problems take their place. For example, it is now accepted
that the Universe started with the Big Bang. But how did
the material from the Big Bang come together to form
galaxies? Today’s scientists can work faster on such
problems with the help of computers. These can solve
mathematical problems in hours rather than the weeks it
would have taken a hundred years ago. Computers also
enable astronomers around the world to link up so they
can work together on our understanding of the Universe.

Tycho Brahe’s
observatory

Astronomers use
computers to analyse
images, to calculate
orbits, and to control
instruments such as
telescopes, satellites,
and space probes.

Find out more

Stars i\278
Constellations p.282
SOIAR SYSTEM P.283
Sun p.284

Telescopes on earth p.297
Telescopes in space p.298
Space probes p.301

296

SPACE

Telescopes on earth

BEFORE THE TELESCOPE was invented, the only way people
could observe the Universe was to look at it with just their eyes.
From 1609, when Galileo first used the telescope to look into the
sky, astronomers have been able to peer farther and farther into
space. They can see surface details on planets and can look at
stars which were once invisible to them. The first telescopes used
lenses to gather the light from stars. These are called refracting
telescopes. Telescopes that use mirrors rather than lenses are
called reflecting telescopes. Today’s telescopes have attachments
that can take measurements and analyse starlight. The telescope
is an astronomer’s best friend.

Comet

telescope images

Images from space (comets, for example) have been
recorded photographically from the earliest days of
photography. Today, astronomers take photographs
through telescopes. The image is recorded on an
electronic chip or photographic plate. Computers may
be used to bring out detail in the image.

Observatories

Telescopes need homes. Usually they
are kept in observatories, special
buildings that are always built high on
mountain tops. This is so the telescope
can obtain the very best view of space -
away from city lights, and high enough
so that Earth’s atmosphere doesn’t get
in the way too much.

Dawn over the enormous reflecting dish
of the Arecibo radio telescope

The Keck Telescope is on the
4,200 m (14,000 ft)
summit of Mauna Kea on
the island of Hawaii.

This peak is home to
an international
collection of
telescopes.

The success of
the multifaceted
Keck has led to
the construction
of an identical
twin, Keck II,
right next door.

Radio image of the
Crab Nebula, taken
by the VLA
telescope

GIANT EYE IN THE SKY

The world’s biggest telescope collects light with a jagged-
looking mirror 10 m (33 ft) across. It would be
impossible to make a single mirror this big, so the
Keck telescope actually uses 36 hexagonal mirrors,
together with extreme accuracy. The Very
Large Telescope in Chile consists of four 8 m
(26 ft) telescopes looking at the same object to
gather the maximum amount of light. Such
instruments can see distant galaxies up to
10,000 million light years away. Because light
takes time to travel this immense distance,
they reveal the Universe soon after it was born.

RADIO IMAGE
Radio waves from space
(sometimes called radio noise)
were First detected in 1931.
However, it wasn’t until the end
of the next decade that radio
telescopes were built and used.
The radio waves are changed into
electrical signals that can be used
to make radio images or pictures.

In New Mexico, the
Very Large Array
(VLA) radio telescope
uses 27 dishes, each
25 m (82 ft) across.

TELESCOPES WORKING TOGETHER
Lots of small radio telescopes can be used
to work like one enormous one. A
combines the information
received by each dish. This
technique is called
terferometry and it was first
used in the 1960s. The
radio telescope of
this type uses dishes
positioned on
different
continents!

RADIO TELESCOPES

To collect radio waves from space, an astronomer uses
a radio telescope. These work like optical telescopes
(that collect light) - a dish faces the sky to collect and
focus the waves. However, as radio waves have a larger
wavelength than that of light waves, a radio telescope
has to be much bigger than an optical one to collect
the same amount of information. The largest single
dish telescope in the world is at Arecibo, Puerto Rico.
Its 305 m- (1,000 ft-) dish is built into a natural hollow
in the jungle. As the Earth moves, the dish points to a
different part of the sky.

Find out more

Opti<

Teli

Reflection p.194
Lenses p.197

CAL INSTRUMENTS

^SCOPES IN SPACE P

p.198

.298

297

SPACE

JUST AS SUNGLASSES protect our eyes, Earth’s atmosphere
prevents a lot of radiation from reaching Earth. It lets light
through, but even this is affected - images are blurred and stars
twinkle, when in reality they shine steadily. For this reason, from
the middle of the 20th century, astronomers have been sending
telescopes into space to get a better look at our surroundings.
These telescopes can see views of the Universe that are
invisible from Earth. They work day and night,
recording data, and transmitting it to
Earth to be analysed. Telescopes enable An x-ray

us to look into space with X-ray,
ultraviolet, and infrared eyes.

image of
the Crab
Nebula

EARLY ATTEMPTS

During the 1930s and 1940s, balloons

were used to carry scientific instruments above most

of the Earth’s atmosphere. Rockets were another

option. Once high enough, they had a few minutes

in which to record a view, such as the Sun in X-rays,

before plunging back down to Earth.

Earth’s atmosphere is divided into different
layers - the troposphere, the stratosphere,
the mesosphere, and the thermosphere.

Different types of radiation get
stopped by different layers.

Gamma rays have the
shortest wavelengths.

UV image
of the Crab
Nebula

IR image of the
Orion Nebula

X-RAY PICTURES
From 1948, when the first X-rays
from space were detected,
astronomers have been looking
at the X-ray universe. X-rays can
reveal “hot spots” or areas of
energetic activity in space. They
can also help us to see otherwise
dim objects such as pulsars.

Ultraviolet rays

INFRARED PICTURES
Although some infrared (IR) rays reach
Earth from space, they get mixed up with
the infrared rays that Earth itself
produces. Therefore, astronomers like to
have infrared telescopes out in space.
These can detect heat sources that light¬
detecting telescopes would not show up.

Thermosphere

X-rays

ULTRAVIOLET PICTURES
Most ultraviolet (UV) light is absorbed by
Earth’s atmosphere (although some gets
through to give us a suntan). Satellites for
collecting UV waves were first launched in
the 1960s. The International Ultraviolet
Explorer (IUE) satellite was used from its
launch in 1978 until 1996.

Longwave ^
radio waves
are collected
in space.

Top of
mesosphere

Shortwave radio
waves reach Earth.

Ozone layer .

Infrared waves get stopped
by a low part of the atmosphere
called the troposphere. A few
penetrate to Earth, where large
telescopes are ready to collect them.

Light waves reach Earth, but they
are blurred by travelling through
the atmosphere.

Radiation

Light waves are just one of
the many types of radiation
that objects in space give out.

Other forms have different
wavelengths. Radio waves, for example, have
a longer wavelength than light waves; X-rays
have a shorter wavelength. Not all this
5 radiation gets through Earth’s

atmosphere to reach the surface - most
light does, some infrared does, but no
amma rays are able to get through.
If astronomers want to collect such
radiation, they must send their
instruments into space.

The Hubble telescope uses mirrors
to collect and focus light and
ultraviolet rays from space.

A computer on board
controls the
telescope and
transmits data to
and from Earth.

HUBBLE
TELESCOPE
The Hubble
Space Telescope
was launched in
April 1990. It orbits
Earth 500 km (310
miles) up in the sky.
From its position, the
Hubble collects images from
millions of years ago, giving
astronomers a chance to see the
young Universe forming after the
Big Bang. The telescope is
maintained in space by astronauts
from the space shuttle.

Earth’s surface

Top of stratosphere
Top of troposphere

Find out more

Electromagnetic
spectrum P.192
Optical instruments p.198
Atmosphere p.248
Telescopes on earth p.297
Rockets p.299
Satellites p.300

Telescopes m space

298

SPACE

Rockets

Anything THAT WANTS TO GET AWAY from Earth must travel in a rocket.
Rockets are used to propel satellites and astronauts into space. Without
them, we would know little about Earth’s surroundings, and we would not
have all the benefits that satellites give our lives. Rockets burn fuel to
make a thrust that pushes them upwards. In fact, most of a rocket
is made up of fuel - its cargo or “payload” takes up a fairly
small amount of room in comparison. In 1903, a Russian
schoolmaster, Konstantin Tsiolkovskii, put forward the
first scientific ideas on rocket propulsion. However,
it wasn’t until 1926, when an American engineer,

Robert Goddard, launched the first liquid fuel
rocket, that space travel was really born.

LAUNCH SITE

Rockets are launched from space centres. There are about
15 of these around the world. Each space centre has
technical and control areas as well as the launch pad
itself. Once everything is prepared, the rocket is
mounted on the launch pad ready for lift-off.

The nearer a launch site is to the Equator,
the more help it gets in lifting off from
Earth’s spin (which is faster there).

VOSKHOD
The Russian Voskhod
rocket was designed to
send more than one
astronaut into space at a
time. In 1964, three Russians
were launched into space. On the
second Voskhod flight in 1965, Russian
cosmonaut Aleksei Leonov became the
first to venture outside the capsule.

Saturn V weighed
over 2,700 tonnes
and so needed an
enormous
thrust to lift off
from Earth. This
was provided by five
engines in its first,
lower stage. Within
minutes, this stage
stopped burning and fell
back to Earth.

Rocket’s nose is shaped
to cut through the air.

Third stage
containing fuel

Stage 3 engine

Apollo
command
module.
This was the
part of the
rocket that the
astronauts eventually
returned to Earth in.

Apollo lunar module
(inside).This was the section
that actually landed on the Moon.

Saturn v

The massive Saturn V rocket was
designed to send people to the
Moon. Not only did it have to get
there, it had to land safely on the
surface, and re-launch back to Earth. Such
a mission requires a lot of fuel. Rockets do
not carry their fuel in one tank, however,
but in several separate containers called
stages. Once one stage is
empty, it drops off to lessen
/fr \ / the load. The fuel from the
next stage is then used.

Rocket fuel usually consists of two liquids - when
mixed, these burn and throw exhaust gases out of the
back of the rocket. This pushes the rocket forwards.

ARLANE

The European Space Agency uses a series of rockets called
Ariane to launch their satellites. As with all space rockets, the
payload - in this case, a satellite - is carried at the nose end.
The larger the Ariane, the bigger and heavier its payload can
be. The extra thrust needed to get into space is provided by the
large boosters strapped to the first stage.

ESCAPE VELOCITY

If you throw a ball into the air,
Earth’s gravity will slow it down
until it eventually falls back. If you
could throw it as fast as 40,000
km/h (24,840 mph), it would be
slowed down, but its speed would
still be great enough to carry it out
of the reach of Earth’s gravity, and
into space. This speed is called
the escape velocity. Rockets
must reach this speed if they
are to escape from Earth.

The force with which a rocket moves away
from Earth must be greater than the force
of gravity pulling it towards Earth.

The German proposed
spaceplane is called Sanger.
It consists of a carrier
aircraft, and a reusable
spacecraft, Horus.

SPACEPIANE
The problem with multi-stage rockets is that
they can only be used once. When the stages
fall back to Earth, they burn up in the
atmosphere and are destroyed. This is why
scientists in several countries are trying to
develop a reusable “spaceplane” that takes
off horizontally. While in Earth’s
atmosphere, it would take in air to burn fuel
(like a normal aeroplane). When in space,
where there is no air, it would burn liquid
hydrogen and oxygen (like a rocket).

Find out more

Gravity p.122
Moon p.288

Telescopes in space p.298
Satellites p.300
Space probes p.301
Humans in space p.302

299

SPACE

Orbits

The path that a \> N
satellite takes \\
arotmd Earth nx

i m i i depends on the job x\

it has to do. For <
j ^ example, the n\

J l geostationary orbit is \
^ j 35,880 km (22,280 miles) ^
above the Equator. Satellites
r in this orbit will complete one
I orbit in the same time that Earth

/ completes its daily spin. So the satellite
* 11,i will always be above the same point on a
Earth. This is useful for television satellites.

The antenna

measures the exact

The solar array
turns sunlight into
electricity.

A radar altimeter
measures the precise
distance down to the
ocean surface below.

Topex/Poseidon satellite

TOPEX/POSEIDON
From an orbit 1,320 km (820 miles) above the Earth’s
surface, this US-French satellite is investigating ocean
currents and wind speeds over the seas.

It has found “sea-level” is not the same
everywhere: the western Atlantic
Ocean is 70 cm (27 in) higher than
the eastern side!

Low-Earth orbit: the
easiest orbit to reach.
It is where the Hubble
Space Telescope, and
the Russian space
station, Mir, orbit.

Polar orbit: circles around
Earth’s poles. Weather satellites
often travel in this orbit as it
enables them to scan the entire
Earth as the planet spins.

Sputnik 1 was an
aluminium sphere
measuring only
58 cm (23 in) across.

SPUTNIK

Russia put the first ever artificial
satellite into orbit in October
1957. During its short time in
space, it investigated Earth’s
atmosphere. Just a month later,
Sputnik 2 was launched. On
board was the first living thing
in space - a dog called Laika.

Satellites

Imagine something looking

down on Earth that could tell us
about the weather or point out areas
such as mineral deposits. Such things
exist. They are called satellites.
There are many different types
of satellite orbiting the Earth, all
performing different tasks.
Navigation satellites help ships or
aeroplanes pinpoint their positions.
Astronomers use satellites to look
out into the Universe. Some satellites
provide us with instant phone calls,
others allow us to watch events
happening around the world “live”
on television.

___ - Eccentric orbit: a satellite measuring

Earth’s magnetic and electric fields will
use this orbit, because it can take
measurements at different
distances from Earth.

REPAIRING SATELLITES
What happens when something
goes wrong with a satellite in orbit?
It can be mended in space by
astronauts. If the fault is a major
one, the satellite is brought back to
Earth for repair and re-launch. In
November 1984, the crew of the
space shuttle Discovery recovered a
telecommunications satellite and
returned it to Earth.

SATELLITE DISH
Once an astronomical
satellite is in orbit, it can
start its work. Ground
stations track the
satellite. They monitor
its condition and
redirect it if necessary.
They also receive and
process the data from
the satellite ready to
pass on to scientists.
Signals from the satellite
are collected by dishes on
the ground. These are
similar to satellite
television dishes but are
much larger.

Geostationary orbit: holds
communication satellites
such as the European
satellite Olympus.

Find out more

Telecommunications p.162
Reflection p.194
Weather watching p.272
Telescopes in space p.298
Rockets p.299
Space probes p.301

300

SPACE

Space probes

Moving through space like roving reporters, space
probes are unstaffed spacecraft that are sent to investigate
and report back on our Solar System. They have made many
discoveries that would be impossible from Earth. Space probes
are highly sophisticated robots. Once launched, they follow a
pre-arranged route to a target, such as a planet. As they fly near
or orbit around the planet, instruments on board set to work.
Results are sent back to Earth by radio. Some of this data is
made into pictures to give close-up views of distant worlds.

The Sun, comets, asteroids, and all the planets except for
Pluto have been visited by different probes.

After discarding its
protective heatshield,
Huygens parachutes
down through Titan’s
lower atmosphere.

The Huygens probe
has a tough exterior
protecting its six
delicate scientific
instruments.
Huygens’
batteries will
last for an hour
on Titan’s
surface. ^

PROBE VISITS

1959 First successful probe,
Luna 2, reaches the Moon.

1962 First successful planetary
probe, Mariner 2, flies by
Venus.

1973 launch of Mariner 10;
first probe to visit two planets,
Venus and Mercury.

1976 Viking 1 and Viking 2
probes land on Mars.

1977 Voyager 1 and Voyager 2
sent to Jupiter, Saturn, Uranus,
and Neptune.

1985 Five probes sen t to
investigate Comet Halley.

1990 launch of Ulysses probe
to fly over the poles of the Sun.

1995 Galileo probe enters
atmosphere of Jupiter

A boom 10.5 m (34.45 ft) long
carries magnetometers, which
measure the strength of Saturn’s
immense magnetic field.

Cassini/Huygens

The international
Cassini/Huygens probe,
scheduled for launch in 1997,
will arrive at Saturn in 2004.
The larger part of the craft, the
American orbiter Cassini, will
tour around the ringed planet.
The small European probe,
Huygens, will be sent into the
dense atmosphere of Saturn’s
largest moon, Titan and land
on its frozen surface.

/Cassini carries 12
different scientific
instruments, and is
controlled by 44
onboard computers.

moon of
Jupiter, was
sent to Earth
by Voyager.

The dish-shaped
aerial sends pictures
and other information
back to Earth.

IMAGES

Space probes provide so much data
that scientists have to analyse it for
years after a craft has finished its job.
Moons of all four of the giant planets
have been discovered by space probes.

Scientists are sure that more smaller
moons are still waiting to be found.

The orbiter continues to
travel around the planet.

The Viking orbiter
and lander separate.

VIKING PROBE
Not only can space probes orbit
around a planet, they can also place
craft - a lander - on its surface.
During the 1960s and 1970s, both
the Americans and the Russians sent
off space probes that orbited and
landed on Mars. The Viking 1 and
Viking 2 probes successfully placed
landers on Mars in July and
September 1976. Between them they
sent back almost 3,000 images,
studied the Martian soil, took
meteorological measurements, and
searched for evidence of life.

VOYAGER PROBES

The twin Voyager space probes, Voyager 1 and Voyager 2, were
launched in 1977. Their task was to find out more about the four
gas giants. They both flew by Jupiter and Saturn. Then Voyager 2
alone travelled on to Uranus and Neptune. Each spacecraft had
11 instruments on board, including two television cameras.

A parachute
slows the fall of
the lander.

Scientists can use
the gravity of planets
to swing a probe
towards its target.

The lander is
released from
the parachute.

The lander touches down
on the surface of Mars.

__ Voyager 1

at Saturn in
November
1980

Voyager 2
at Saturn in
August 1981

Voyager 1 at
Jupiter in March
1979; Voyager 2
in July 1979

Voyager 2
at Uranus
in January
1986

Find out more

Voyager 2 at
Neptune in
August 1989

Robots p.176
SoiAR SYSTEM P.283
Sun p.284

Telescopes on earth p.297
Telescopes in space p.298
Satellites p.300

301

SPACE

TRAINING FOR SPACE
For journeying into space, astronauts
need to be physically and mentally fit.
They undergo very long and hard
periods of training in conditions that
are similar to those in space. For
example, astronauts may train in large
swimming pools so that they have some
idea of what feeling weightless is like.
They wear special suits and practise
the jobs they will do in space.

FOR CENTURIES, humans have dreamed of
travelling in space. But the dream only became a
reality in 1961 when a Russian astronaut called Yuri
Gagarin rocketed into space and orbited around
the Earth. Today, many men and women travel
into space; most go just for a few days, but others
go for months at a time. Even so, space remains a
hostile environment for humans. Spacesuits are
needed for protection and to provide air to
breathe. If humans are to live and work more
permanently in space, and to land on Mars in the
next century, we must learn all we can about the
long-term effects of space travel.

There are lights on
the helmet so that
the astronaut
can see.

A camera on the
astronaut's shoulder
takes pictures as he or
she moves around.

The upper half
of the suit is a
hard shell of
fibreglass.

Under the helmet is a cap with
headphones and microphones
for communication with
Earth and with
astronauts
in the craft.

iVliVlU

A manned manoeuvring unit
(MMU) is a cross between a
backpack and a chair. It runs on
nitrogen and can be recharged
from the spacecraft. The astronaut
controls the MMU from the arm¬
rests. This unit was first used by the
American astronaut Bruce
McCandless in February 1984.

T o keep cool, astronauts
wear an undergarment fitted
with water cooling tubes.

SALLY RIDE

Until 1983, all the
American
astronauts were
male. When the
Space Shuttle
programme was
introduced in
the 1970s, both men and
women could apply to be
astronauts. In 1983, Sally Ride
became the first American
woman in space, and in 1991
Helen Sharman became the first
British astronaut.

Spacesuits
provide 100%
oxygen for
breathing.

Underneath the suit is a urine-
collection device which is emptied
on return to the spacecraft.

WOMEN IN SPACE
The United States and the Soviet
Union dominated the first two
decades of space exploration. In
1963, the Russian astronaut
Valentina Tereshkova became the
first woman to travel into space.

Space wear

The first astronauts had just one
spacesuit per journey. But today,
astronauts wear different clothes
for the different jobs they do.
One suit is for travelling to and
from space. Then, in orbit, they
wear specially designed casual
clothes. If they are working
outside their spacecraft, they
wear a suit called an
extravehicular mobility unit
(EMU). On top of this is a
strap-on motor called a
manned manoeuvring unit
(MMU) that can fly the
astronaut around.

Spacesuits are cleaned and
dried on return to Earth ready for
another flight. A spacesuit should
last for about eight years.

On 20 July 1969, Neil
Armstrong became the
first human to step on
anything other than
the Earth. His
colleague Buzz
Aldrin joined him 19
minutes later.

MOON MISSIONS
During the late 1950s, there was a race to conquer
space by sending up the first satellites and then
humans: the space age had begun. In 1961, the
Americans promised to land a man on the Moon by
die end of the decade. They did. In 1969, Neil
Armstrong became the first person to walk on the
Moon. Between 1969 and 1972 astronauts spent
nearly 80 hours on the Moon’s surface.

Humans in space

302

SPACE

Find out more

Gravity p.122
Solar system p.283
Rockets p.299
Satellites p.300
Space probes p.301
Space stations p.304

monitoring

astronauts

In March 1992, Russian
astronaut Sergei Krikalev
returned to Earth after
spending 313 days in space.
On his return, his physical
health was closely
examined. In space,
astronauts can expect their
heartbeat to slow and to
suffer from space sickness.

Sergei

Krikalev

After landing, new
fuel tanks are fitted
for the next launch.

Living in space

Space travel has changed since Yuri Gagarin’s day. In orbit,
astronauts move about their craft in casual clothes and eat their
favourite meals. When they are not working, they relax with
taped music and a good book. They even take it in turns to do
“housework”. But all of this is done in a state of weightlessness.

As bodies are not working against gravity, bones and muscles may
weaken (which is why astronauts must exercise every day). So far,
the effects of weightlessness on the human body have reversed
once the astronaut is back on Earth. But scientists are monitoring
the effects as astronauts spend longer and longer in space.

space,
liquids are
very difficult to

WEIGHTLESSNESS conlroL This water has

r-w-i, . . formed into a floating ball.

The gravity or Earth

continually pulls on our bodies to give us weight.
But if you are in a lift that is speeding
downwards, you feel lighter. This effect is
exaggerated in a spacecraft; as it is falling in a
gravitational field, the astronauts inside it are
falling at the same rate and become weightless.
Experiments on animals and plants are carried
out in space to learn of the effects of
weightlessness. Certain experiments, impossible
on Earth, can also be performed.

The orbiter leaves
its orbit tail first.

A thermal protection system
enables the orbiter to survive the
high temperatures it encounters as
in it re-enters Earth's atmosphere.

SHUTTLE JOBS
The Space Shuttle is very
versatile. It can be used for
launching satellites, for
servicing them, and for
retrieving them for return to
Earth. Not only this, it is used
as a laboratory in space, and
can also transport space station
parts into space for assembly. A
shuttle mission lasts around
seven days, and has a crew of
up to eight people.

A braking system brings
the orbiter to a halt.

The unpowered orbiter glides
back to Earth, and lands on a
runway like a plane.

In space, astronauts may
feel dizzy and sick as
their bodies move
around.

Astronauts suck drinks through straws but eat
snacks such as chocolate or nuts in the usual
way. Meals are oven warmed before
being placed in a special tray to
stop them floating away as
they are eaten.

Most
foods are
dehydrated -
the astronauts
just add water before
eating. Other foods are
sealed in tins or pouches just as
on Earth. Fresh food may be
available for the first part of a trip.

SPACE SHUTTLE

The first astronauts were sent into space in small capsules that
sat on top of rockets. They returned by splashing into the sea.
These missions were expensive as the rockets could only be used
once. Today, American astronauts are transported into space by
the Space Shuttle. The main parts - the orbiter spacecraft, and
the rocket boosters - are reusable. The orbiter returns to Earth
like a plane, and can be used over and over again.

303

SPACE

Space stations

TRIPS INTO SPACE need no longer be short stays. Astronauts can now
stay in a space station. This is a large satellite orbiting around Earth with
room on board for people to both live and work for weeks or months at
a time. In the future, it will also be used as a hotel where astronauts can
stay before travelling farther into the Solar System, or before coming
back to Earth. Space stations are important because experiments in
microgravity (conditions of very low gravity) can be carried out there
by a person rather than a machine. The astronauts also perform
experiments on themselves to see how humans cope in space.

In the main American laboratory,
astronauts perform experiments in
microgravity. They will make a wide
range of new materials here.

SKYIAB

For five years in the 1970s, Skylab,
the first American space station,
became a “drop-in” centre for
visiting astronauts. Skylab was the
size of an average house. It offered
astronauts the first chance of
comfortable surroundings
in space.

International Space Station

The world’s first multinational base in space is being
launched in segments from 1997 through to 2002. It
is being built by the American space agency
NASA, the Russians, the Japanese, and the
European Space Agency. End to end it
stretches 88 m (290 ft), with a “wingspan”
across its solar panels of 110 m (361 ft).
The International Space Station flies
407 km (220 miles) above the Earth,
{' and is home to six crew.

The photovoltaic array
converts sunlight into
electrical power.

For safety reasons,
the huge solar
panels are sited i

well clear of the j

docking ports.

The Russian section: these modules are
the first to be launched, and have their
own power supply and crew quarters.

The large
concertinaed
panels keep the
International
Space Station
cool __—

The module from the Japanese
space agency (NASDA) ends
in an exposed pallet, for the
experiments that need to be
exposed to space.

\ The habitation
module is where
N European astronauts relax,
The US Space module eat, and sleep.

Shuttle will transport *

crew members to and

from the space station. T|

Russian Soyuz >( j
capsules act as
“lifeboats", allowing
the crew to return to
Earth immediately in
case of emergency.

SPACE STATIONS

1971 First Russian space
station is launched. It is called
Salyut.

1973 First American space
station is launched. It is called
Skylab.

1980 Skylab re-enters Earth’s
atmosphere and disintegrates.

1983 First purpose-built space
laboratory is launched. It is
called Spacelab.

1986 The largest space station,
Mir, is launched from
Baikonur in Russia.

In the laboratory
module, the crew
experimented in
microgravity
conditions.

Towering solar
panels supplied
Mir with electricity.

EXPERIMENTS
Chemists, biologists, and
physicists will all benefit from
having a laboratory in space. They
will be able to work in conditions
of microgravity, where they can
process and produce materials
(such as drugs or electrical
components) to a level of purity
that is not possible on Earth.

The crew
lived in the
main module.

The manned Soyuz
capsule carried crew
to and from Mir. The
unmanned craft,
Progress, brought
supplies.

MIR

The Russian space station,
Mir, was launched in February
1986 and boarded by astronauts
three months later. Spacecraft
take astronauts to the station by
docking (connecting) with one
of its six ports. At present, the

1988 Russian cosmonauts
Musa Manarov and Vladimir
Titov return from 366
days in space.

Handrails helped
the crew working
outside Mir, as they
repositioned the solar

CiRAVITY P.122

Satellites p.300

Find out move

Photograph of solar prominence
taken from space station Skylab

arrays and exposed
some experiments to
space conditions.

station has room f or up to six crew,
but the station’s size can be changed by
adding new modules to the basic structure.

Space probes p.3()1
Humans in space p.302

304

LIVING THINGS

FRIEDRICH
WOHLER

All living things
contain carbon
compounds. Until the
19th century, most
scientists believed that
carbon compounds in
living things were quite
separate from those in non¬
living things. But in 1828, the
German chemist Friedrich Wohler
(1800-82) disproved this idea, which
was known as “vitalism”. He made
urea, a carbon compound formed
by animals, from a compound that is
found only in non-living matter.

Moths from the Arctiidae family

HOW BIOLOGISTS WORK

During the I9lh century, scientists often studied animals by
killing and collecting them. These moths arc part of a typical
museum collection that contains thousands of specimens.
Collecting can provide useful information, but it can also harm
rare species. Because today’s biologists are more aware of the
need for conservation, they spend more time studying animals
in the wild. In this way, they can learn about an animal without
harming it or changing its natural behaviour.

Fern

Organisms and species

To biologists, the word “organism” means anything that is
alive. A bacterium (singular of bacteria) is an organism, and so
too is a plant, an insect, or a human being. Another word that
is often used in biology is “species”. A species is a group of
organisms that are able to breed with each other, such as lions
or ostriches. The organisms above belong to different species.
They can breed with members of their own species, but not
with members of any other species. Organisms usually live
separately, but sometimes members of the same species live
together very closely in a colony
(large group).

HIDDEN LIFE

Although this plant looks quite lifeless,
it is actually very much alive. Lithops
(Lithops nucampiae ), known as the
“living stone” plant, grows in dry parts
of southern Africa. For most of the
year, the Lithops plant is well
camouflaged. But it has to reproduce.
To do this, it grows brightly coloured
flowers. These flowers attract insects
that transfer pollen from one plant to
another. After the plant has been
pollinated, it produces seeds.

EXPLORING NATURE
The English naturalist Henry Bates (1825-92)
was one of the first European people to
investigate the wildlife of the Amazon rainforest
in South America. He collected many new
species and studied the ways in which they
compete for surv ival. Today, scientists are still
discovering new species. At the same time,
many species are becoming extinct because of
the damage we are doing to the natural world.

YOU WILL FIND living things almost
everywhere you look. A single crumb of bread
can support a tiny mould. A spoonful of river
water may be home to many different
microscopic forms of life. Living things are
spread across vast land masses and throughout
the oceans between them. Even where
conditions seem extremely hostile - in
scorching dry deserts, or on freezing
mountain tops, for example - some forms of
life survive and multiply. Biology is the study
of all living things, from those that can be seen
only with a microscope to those that are much
bigger than we are. Biologists study living
things to find out how they work and how they
are linked together in the complex pattern of
life on Earth.

Bacteria

Beetle

Fungus

305

LIVING THINGS

What is life?

LIVING THINGS EXIST in many different shapes and sizes. They
range from trees that are higher than a 20-storey building to
bacteria that are far too small to see. Plants spend their lives in the
same place, but many animals travel huge distances through the air,
over land, or in the sea. Despite these differences, all forms of life
share some important characteristics. They all take in raw materials,
either in the form of food, or in the form of simpler substances.
They all use chemical reactions to get energy from these raw
materials, and they all make waste products from this process.

The energy they obtain enables them

to grow, to reproduce, and to Chemical reactions

0 1 inside a mouse’s body

respond to the world enable it to move and

around them. iTAmEW U : staywarm

PI ANT LIFE

Plants cannot move about, but they are just as
alive as we are. An oak tree collects energy from
sunlight, and builds it into food. It uses this
food to grow and to reproduce. Although the
tree does not have any special sense organs, it
can detect and respond to light.

This shell was once home to a
nautilus - a mollusc that lives in
the sea. As the mollusc grew, it
made sure the shell grew too by
secreting calcium, which gradually
crystallized to form
new shell.

ORDER FROM CHAOS

A wind-up toy will gradually
lose its energy if you do not
turn its key. After a few
years, it may also rust and
break. It is typical of non¬
living things. Living things
work the other way around.
They take in energy, and
use it to build structures
such as cells or shells. This
ability to create order from
chaotic matter is unique.
Only living things can do
this. When they die, this
ability is lost.

energy and
nutrients from
food to grow.

PLANKTONIC LIFE
Most forms of life are far smaller
than we arc. These tiny
planktonic organisms drift with
the currents in the open sea. Each
member of the plankton is very
small, but together they weigh
millions of tonnes.

Characteristics of life

The most important daily task for these mice is to find food
to fuel their bodies. They use their senses to track down
anything they can eat, and to check for danger. A mouse
obtains energy by combining its food with oxygen. When it
does this, carbon dioxide is formed as a waste product. It also
uses the nutrients in food to build new body parts. Within six
weeks of being born, a mouse is ready to reproduce.

A female mouse
the energy and nutrients
(raw materials) from
food to make milk for
her young.

mouse takes in
oxygen and gives
out carbon dioxide
as a waste product.

shape is
fixed - it
cannot
grow or
develop
without
human
help.

LIFELESS MACHINE
Robots may seem to be alive, but they
are really just complicated, non-living
machines. It is true that a robot
can use energy to move. But it
cannot get this energy on
its own - it depends on
people. Not only this, it cannot grow
or reproduce. Without regular
maintenance, a
robot will
eventually
break down
and fall
apart.

Find out more

Photosynthesis p.340
Nutrition p.342
Celluiar Respiration p.346
Internal Environment p.350
Growth and Development p.362
Asexual Reproduction p.366
Sexual Reproduction p.367

306

LIVING THINGS

HOW LIFE BEGAN

OuR PLANET has been around for about 4,500 million years. In
its early years, it was far too hot and dangerous to support life. It
was bombarded by meteors and torn apart by volcanic explosions.
But as the Earth cooled, its surface became calmer. Steamy water
vapour from the constant eruptions formed clouds and rain fell.

In this water, life appeared over 3,500 million years ago. Some
people believe that living things were specially created, but most
scientists think life came about through a series of chemical
reactions that happened by chance. Over millions of years, these
reactions slowly built living things from simple chemical substances.

OLDEST LIFE FORMS
These cyanobacteria are
simple forms of life that
live like plants. They
usually live in shallow
water, and make
their food by
photosynthesis.
Geologists have
found fossilized mats
of cyanobacteria that
date from 3,500 million
years ago. These life forms
must have been among the
earliest on Earth.

^ y ■

?/ \

RAW INGREDIENTS
The ocean and atmosphere of the early
Earth contained simple chemicals, such
as water, methane, ammonia, and
hydrogen. In their famous experiment,
Urey and Miller sealed a mixture of
these chemicals in a container. They
wanted to see what would happen when
the chemicals were allowed to react.

Water,
methane,
ammonia, and
hydrogen chemicals were
sealed in a container.

Energy
produced by
electrical spark
caused chemicals in
container to react with
each other.

RESULTS

After running the experi¬
ment for a week, Urey and
Miller found that several new

Urea, a common
waste product of
living things

Glutamic
acid, an
amino acid
used by living
things to build
proteins.

and complex substances had

formed. Among them were amino

acids. These are important chemicals

that link together to form proteins, the building

blocks of life.

LIFE FROM LIFE

At one time, people thought that
living things could suddenly appear
from lifeless substances.They
thought, for example, that maggots
developed from decaying meat.
Experiments by Italian scientist
Lazzaro Spallanzani (1729-99) and
French scientist Louis Pasteur
(1822-95) showed that this idea was
wrong. Living things are now always
formed by reproduction.

By laying her eggs on meat, this female bluebottle
//y (Calliphora vomitoria) ensures a plentiful supply
of food for the maggot larvae when they hatch.

Cradle of life

Imagine a young Earth covered with oceans
that contained simple chemicals. Energy from
sunlight and from strikes of lightning would
have made these chemicals react with each
other. Eventually, some of these reactions may
have created chemicals that could copy them¬
selves, or membranes (coatings) that would
shield them from the outside world. In 1953,
American chemists Harold Urey and Stanley
Miller tested this idea. They found that complex
substances could be built up from simpler ones.

LIFE BEYOND EARTH?

If life arose on Earth by
chemical reactions, it is
possible that it also evolved
elsewhere. In 1996, American
scientists announced that
they had found fossils of
micro-organisms in a
meteorite from Mars. Not
all scientists are convinced
that the structures are fossils,
or that they formed before
the meteorite reached Earth.

However, if the findings
are confirmed, this will
show that life has arisen
elsewhere in the Universe.

•W. T

Original chemical
attracts other
chemicals and
reacts with
them.

►

After several
reactions, a
copy of the
original
chemical is
formed.

CHEMICAL REPRODUCTION
Life may have started in a simple
way. By chance, a chemical may
have entered into a series of
reactions that resulted in it
making a copy of itself. This copy,
through the same reactions, could
then make a copy of itself. The
chemical was able to reproduce.

Find out more

Carbon p.40
Hydrogen p.47
Earth p.209
Cells p.338
IOTOSYNTHESIS P.3
GENETICS P.364

307

LIVING THINGS

These colours are
imaginary. Nobody
knows what colours
Archaeopteryx was.

Archaeopteryx had
peg-shaped teeth, just
like those of reptiles.

Evolution

Chicken-size

body

Feathered,
long front legs

reptile-like
tail

Reptile or bird?

Very occasionally, a fossil is
found that shows how one major
group of living things may have evolved
from another. One such fossil is that of
Archaeopteryx , which means “ancient wing”. The
fossil shows an animal that had scales and teeth
like a reptile, but that also had feathers like a bird.
From this evidence, biologists can be almost
certain that birds evolved from reptiles.

Imagine being able to go back in time to see what

living things looked like millions of years ago. Sadly, this is
impossible, but we can find out a lot about the past by
looking at fossils. A fossil is created when something that
was once alive becomes buried by mud or sand. The soft
parts of the plant or animal often rot away without trace,
but the harder parts, such as stems, bones, teeth, and
shells, very slowly turn to stone. Fossils from all over the
world show that living things have gradually changed over
many millions of years. Some kinds have become extinct

(ceased to exist), and new
kinds have developed
from older ones.
This process of slow
change is called
evolution.

FOSSIL RECORD
This Archaeopteryx fossil was
found in Germany in 1861. It is
thought that Archaeopteryx evolved
from small dinosaurs (a type of
reptile) that ran on two legs.

EVOLUTION OF THE HORSE
Fossil evidence shows that the modern
horse has evolved f rom smaller ancestors,
which lived quite differently. The earliest
horse, Hyracotherium, was about the size of a
small dog. It had four-toed hooves on its
front feet and browsed on the leaves of

- Find out mare -

Fossils p.225

How EVOLUTION WORKS P.309
Classifying living things p.310
Reptiles p.330
Birds p.332
Genetics p.364
Factfinder p. 420

bushes. Over millions of years, its
descendants became bigger, and their diet
changed from leaves to grass. They
developed longer legs with fewer toes,
enabling them to run away from their
enemies on open grassland.

Hyracotherium lived
over 50 million years
ago. It probably hid
from its enemies
because it was small
and could not run fast.

Mesohippus, which
lived about 30 million
years ago, had longer
legs and just three toes
on its front feet.

Merychippus appeared
about 20 million years ago.
It was the first horse to eat
grass. It also had three
toes, but one of the toes
formed a large hoof.

Equus, the modern horse,
evolved about 2 million years
ago. It lives on grass, and it has
just a single toe on each foot,
forming a hoof.

GEORGES-LOUIS
BUFFON

In the 17th century,
most people believed
that living things had
been specially
created. They thought
that each kind of plant
or animal had fixed
characteristics, a view still
held by some people today. Count
Georges-Louis Buffon (1707-88) was
a wealthy French naturalist who
gradually came to doubt this idea.
During research for his 44-volume
work Natural History , he decided that
some species of plants or animals
must have given rise to others. He
was one of the first people to write
about the idea of evolution.

A SHARED PATTERN

Evolution works by adapting things that already exist.
One species may evolve into others that look very
different, but they all share the same basic pattern.
Mammals are a good example. They have front limbs
of many different shapes and sizes, and they carry
out many different functions - from swimming
to flying. But each one is built on the same
basic pattern. This suggests that
mammals have evolved from a
common ancestor.

A human arm contains two
sets of long bones. The
hand is made up of five
sets of finger

porpoise’s
front flipper
contains two
sets of short
“arm" bones,
and five sets of ‘linger”
bones.

A bat’s wing
contains two sets of
“arm" bones, and is
stretched out by five sets
of long “finger" bones.

308

LIVING THINGS

HOW EVOLUTION WORKS

WHY SHOULD PLANTS or animals slowly
change as one generation follows another? Two
19th-century biologists, Charles Darwin and
Alfred Russel Wallace, quite separately hit upon
the answer. They knew that members of a species
vary from each other slightly, and that these
differences can be passed on to the next
generation. They also knew that all living things
have to compete for resources, such as food.
Darwin and Wallace realized that the young born
with the most useful differences would produce
the most offspring. As a result, the species would
evolve, or become better adapted to its way of life.
This process is called natural selection.

Tool-using finch holds a cactus
spine in its beak to pick out insects
from bark crevices.

War bier finch has
a sharply pointed
beak. It feeds
entirely on insects.

Large ground
finch eats mainly big

seeds. It cracks them

Small
tree finch eats
insects. It uses its fine beak to
snap them up.

Vegetarian
tree finch has a curved beak. It
eats buds and leaves.

Cactus
ground
finch has a
sharp beak. It
eats mainly seeds, but
also some insects.

Galapagos finches

During a round-the-world voyage on board I IMS Beagle , Charles
Darwin landed in 1832 on the remote Galapagos Islands, off the west
coast of South America. Here he saw many unique animals, including
13 species of finch. Darwin studied the finches carefully, noting their
similarities and differences. It became clear to him that they must all
have descended from one species of finch that had arrived from the
mainland. The original finch ate seeds and lived on the ground, but its
offspring had gradually evolved different beak shapes and different
ways of life. Seed-eating finches usually have big, powerful beaks, while
insect-eating finches have thinner, pointed beaks.

STRUGGLE FOR SURVIVAL
This female spider laid hundreds of
eggs. Not all of the baby spiders
survived, and more will die
they can reproduce. If
these spiderlings did not
have to compete for food and
shelter, the world would soon be
overrun by spiders!

Adult spider carries
her offspring around
on her back.

ARTIFICIAL SELECTION
Variations within a species do not
always happen naturally. The stripes
on these flowers are artificial - they
were brought about by exposing a
plant to X-rays. The X-rays changed
the plant’s own chemical
“blueprint” (genetic make-up), so
that the stripes were passed on to
the next generation. The stripy
characteristic can be made more
common by deliberately breeding
these plants. This way of spreading
changes in plants and animals is
called artificial selection.

Wallace

CHARLES DARWIN
AND ALFRED
RUSSEL WALLACE

The theory of natural
selection, also called
“survival of the fittest”,
was conceived by
Darwin (1809-82)
and Wallace (1823-1913).

Before they published their
work in 1858, many people
thought that plants or animals,
evolved by changing during
their lives. It was thought that
these changes were passed on to
offspring by their parents, causing Darwin
evolution. Darwin and Wallace put forward
evidence to support the theory of natural
selection. In 1859, Darwin outlined this idea
in his bestselling book, The Origin of Species.

EVOLUTION OF THE FLEA
Natural selection does not always
make things bigger or more
complicated. It often “doubles back”
on itself. Long ago, the ancestors of
fleas evolved wings. But wings are
not particularly useful to fleas. As a
result of natural selection, fleas have
lost their wings. Instead, they have
developed powerful back legs so that
they can leap aboard their hosts.

Rabbit flea (Spillopsyllus
cuniculi) feeding on a rabbit.

on petunia are
a result of artificial
selection.

Find out more

Birds p.332
Movement p.356
Genetics p.364
Sexual reproduction p.367
Deserts p.390
Fact finder?. 420

LIVING THINGS

Long BEFORE BIOLOGY became a science,
people used ordinary names for common plants
and animals. These names usually described
what somethin? looked like, where it was

This chart shows some of
the animal kingdom phyla.

KINGDOM ANIMALIA
The animal kingdom is one of five major
groups of living things. The kingdom is
divided into about 30 groups. Each group
is called a phylum. Some of these groups
contain many species, while others contain
just a few. The Roman snail belongs to the
mollusc phylum, or Phylum Mollusca.

krthropods

ichinodermj

innelids

Cnidarians

vary between languages. Even in one
age, some things have several names,
) while others have none. The 18th-century
/ Swedish botanist Linnaeus devised a way of
naming living things and classifying them
into groups. In his binomial (two-part) system
of classification, every species has its own name. As
well as identifying the species, it also shows where

it fits into the world
of living organisms.

Platyhelminthes

Others

*Fishj\
/(Birds) \
/(Reptiles)
(Mammals)
(Amphibians)
^hordates ^

.Molluscs

lematodes

/ PHYLUM MOLLUSCA
The mollusc phylum
contains about 90,000
species, making it one of
the l ar g est phyla (plural of
phylum) in the animal kingdom.
A mollusc has a special body layer,
called a mantle, that can produce a shell.
The mollusc phylum is divided into seven groups
called classes. The Roman snail belongs to the
Class Gastropoda, which means “stomach-foot”.

Heb. Reem, Rhinoceros, Neieshoom .

NAMES TO REMEMBER
Even before Linnaeus devised
his binomial system, educated
Latin to

people were using
name plants and animals.

This engraving of a
rhinoceros appeared in a
medieval “book of beasts”.

CLASS GASTROPODA ^
Gastropods have a single, sucker-like foot,
and most move by creeping along on it. The g
majority have well-developed heads, and eyes |§
on tentacles. The Class Gastropoda consists of
three subclasses. The Roman snail has a lung,
and so is a member of the Subclass Pulmonata,
which means “with lung”.

SUBCLASS PULMONATA
4 - The Subclass Pulmonata is split
into two groups, called orders. The
Roman snail lives on land. It has eyes
I at the tips of its tentacles, and so is

r / included in the Order Stylommatophora.

CHANGING NAMES J

Scientific names often change as
biologists find out more about how
living things are related. The bluebell
was originally named by Linnaeus, who
included it in the genus Hyacinthus. It
has been renamed many times as a
result of scientific studies, and it is now
classified as belonging to another
genus, Scilla.

Classification

Here you can see how one
species, the Roman snail, is
classified. As you work down
the page, you will notice that
the classification starts with
the animal kingdom, and
then narrows down until it
picks out just one species -
according to various
characteristics. These
categories have been devised

SPECIES Helix pomatia

ORDER

STYLOMMATOPHORA
This order contains many
kinds of air-breathing
molluscs that live on land
and that have eyes on
tentacles. It is divided
into several groups, called
families. These include

FAMILY HELICIDAE

In biological
classification, a family
means a collection of
species. Within a family,

GENUS HELIX

The genus LMxcontains many species that arc

Classifying living things

by biologists, and work like
divisions in a vast filing
system. Biologists often use
additional divisions, such as
subphylum and superorder,
that are not shown here.

families of both snails and
slugs, which are similar,
although most slugs do
not have a shell. The
Roman snail belongs to a
family of snails called the
Helicidae.

there are groups of
species called genera
(plural of genus). The
Roman snail belongs to
the genus Helix because
of its shell’s helical
(coiled) shape.

very similar. Each one has a binomial scientific
name. The first part of the name identifies the
genus that all the species belong to - in this case,
Helix. The second part identifies the species itself.
The species name of the Roman snail is pomatia,
meaning “ apple-shaped”. The Roman snail’s full
scientific name is therefore Helix pomatia.

310

LIVING THINGS

PLANTS ANIMALS

MONERANS

The moneran kingdom
consists of the single-celled
organisms, bacteria, and the
blue-green algae called
cyanobacteria. A moneran
cell is prokaryotic (simple,
with no nucleus). All other
living things have eukaryotic
cells that have a nucleus.

PROUSTS

The protist kingdom is made
up of organisms that have a
single eukaryotic cell. Protists
are extremely varied. Some
biologists include single-
celled algae in this kingdom,
while others think that they
belong to the plant kingdom.

FUNGI

The fungi kingdom consists
of organisms that absorb
substances originally
produced by other living
things. Fungi are sometimes
treated as if they were plants.
However, the structure of
their cells and their way of
life are quite different.

The plant kingdom contains
organisms that use
chlorophyll (green pigment)
to harness the energy in
sunlight in order to make
food. Plant cells have rigid
walls made of a substance
called cellulose.

The animal kingdom contains
organisms made of many
cells that live by taking in
food. Most animals can
move, but some spend a
large part of their lives
anchored to one spot. Their
cells do not have rigid walls.

Eupholus

beccarii Julodis klugi Helaeus

subserratus

Heterorrhina

macleayi

Animals with
short necks

Animals with
long necks

Five kingdoms of living things

At one time, biologists divided the living world into just two
groups: the plant kingdom and the animal kingdom.

Telling the difference between a plant and an animal
seemed easy. Plants were green, rooted in one place, and
needed light to live. Animals usually moved about, and fed
by eating other things. However, biologists have since
discovered that the living world is not that simple. In any
handful of soil, or bucket of water, there are vast numbers
of tiny living things that do not belong to either kingdom.
Today, the living world is usually divided into five kingdoms.
As ideas change about how living things are related, the way
that they are classified changes too.

Lion

Peacock

Animals that walk on two legs

Animals with long tails

CHOOSING A NAME
The first person to
discover a new species
often has the honour of
choosing its name. This is the
skull of a dinosaur called Baryonyx xvalkeri. The
first part of the name refers to the dinosaur’s
heavy claws. The second part commemorates
the discoverer - Bill Walker.

IMPORTANT CHARACTERISTICS
The first family tree suggests that
an ostrich is more closely related to
a human than to a peacock.
Common'sense tells you that this is
unlikely, because ostriches and
peacocks both have feathers and
beaks, while we do not. The family
tree above is more sensible. It is
based on features such as feathers
and bone structure, which give a
much better guide to classification.

Human

Lion

Peacock

HOW MANY SPECIES?

Biologists still have no real idea how many species of
living things exist on Earth. Almost two million have
been discovered and described, but there may be ten
times that number. We know of about 550 species of
conifers, and nearly 400,000 species of beetles.

Animals with eyes
that face forwards

UNIMPORTANT CHARACTERISTICS
Biologists try to classify species in a way that shows
how they are linked through evolution. To do this,
they have to choose characteristics that different
species share. But which characteristics are the most
important? The family tree above shows one way of
classifying four animals, based mainly on their shape.
It does not work very well.

Animals with feathers

These are just five of the
thousands of beetle species.

Tachelophorus
giraffa

Animals with eyes
that face sideways

Human

Animals with fur

Non-flying animals

Flying animals

Animals with hands

Animal with paws

- Find out more -

Evolution p.308
How EVOLUTION WORKS P.309
Molluscs p.324
Cells p.338
Photosynthesis p.340
Skeletons p.352
FactFinder p.420

311

LIVING THINGS

Head

Collar

Bacterium makes
copies of the
virus’s DNA.

Viruses

Empty viruses attached to
outside of cell.

The UNPLEASANT SYMPTOMS of a cold are caused by a virus that
attacks your nose and throat. A virus is a tiny package of chemicals
coated by protein that breaks into living animal or plant cells. Once
inside, it “hijacks” the cell’s chemical processes, so that instead of
working normally, the cell makes copies of the virus. Scientists do
not consider viruses to be fully alive because they cannot reproduce
on their own - they need the help of living cells. As well as the
common cold, viruses cause many other diseases. These include
chicken-pox, mumps and measles, and also AIDS (Acquired
Immune Deficiency Syndrome), which is thought to be caused by
HIV (Human Immunodeficiency Virus). This
virus puts the body’s natural defences out
of action, so that other viruses or
bacteria can attack.

Protein

- ./

BACTERIOPHAGES

Some viruses, called bacteriophages,

attack bacteria in order to reproduce.

This bacterium has been attacked by T4
bacteriophages. Empty viruses, which have
injected their DNA (deoxyribonucleic acid)
into the bacterium, are
attached to the out¬
side of the cell.

HOW VIRUSES ARE COPIED
The T4 bacteriophage virus
looks like a miniature
spaceship. It forms copies of
itself by injecting its DNA into
a bacterium. The DNA makes
the bacterium build all the
parts needed to assemble
new viruses. The parts are
then put together, and the
new viruses break out of
the bacterial cell.

Double strand
of DNA

Herpes virus

Chicken-pox, shingles, and cold sores are caused by herpes viruses.
Inside each virus is a double strand of the genetic chemical DNA. This
contains all the “instructions” needed to make a living cell produce
copies of the virus. The DNA is protected by a case made of protein,
which has 20 identical sides. Around the case is a coating called an
envelope. When the virus encounters a suitable cell, its
envelope links up with the cell’s membrane - rather like two
bubbles joining together. The rest of the virus then enters
the cell, where it is copied. Herpes viruses sometimes live in
the human body for many years without causing any harm.

and
bacterium.

Streaky

tulip

petals

SMALLER AND SMALLER

Viruses are not the only chemical particles that can
infect living cells. Viroids are similar to viruses, but they
are even smaller. A viroid is made of a short length of
the genetic chemical RNA (ribonucleic acid),
without a protein coat. Prions are smaller still. Unlike
viruses or viroids, they are thought to be made of
proteins. Viroids cause several diseases of plants, while
prions cause scrapie, a disease of sheep and cattle.

Part of a bacterium

Viroid

Prion

T4 bacteriophage
virus

RUNNY NOSES
Cold viruses give
you a “runny
nose”. When you
sneeze, droplets of
moisture containing
millions of viruses are
sprayed into the air.

If someone close
breathes in some of
these droplets, they
may catch the cold
as well.

Vase of Flowers by Jan van Huysum
(1682-1749).

TREASURED VIRUS
Tulip mosaic virus creates beautiful
streaks in the petals of tulips. In
17th-century Holland, tulips
infected with this virus were highly
prized. People traded tulips like
stocks and shares, and the price
of a single tulip bulb was often
more than an ordinary person’s
yearly income.

Find out more

Bacteria p.313
Cells p.338

Internal environment p.350
Growth and development
p.362

Genetics p.364

312

LIVING THINGS

BACTERIA

Find out more

Cells p.338
Photosynthesis p.340
Teeth and Jaws p.344
Internal Environment p.350
GROwrH and Development p.362
Factfinder p.420

ROBERT
KOCH

A German
doctor named
Robert Koch
(1843-1910) helped
to establish the study of
bacteria as a medical
science. In 1876, he
discovered that the
bacterium that produced
anthrax, a disease of cattle
and humans, could be
cultured (grown) in a
laboratory. He also
identified the bacteria
that cause tuberculosis
and cholera.

If YOU HAVE EVER LEFT MILK OUT in warm weather, you will
know how quickly it turns sour. This change is caused by the rapid
growth of microscopic moneran organisms called bacteria.
Bacteria are the most widespread living things on Earth. They are
found in the air, in the ground, and all over plants and animals,
including humans. A few kinds even live in hot springs and ice.
There are many different bacteria - some
harmful, some very beneficial. Harmful
bacteria include those that cause
dangerous diseases, such as tetanus
and septicaemia (blood poisoning).

Beneficial bacteria include those
that break down waste, and those
that live in plant roots, gathering
nitrogen from the air.

Bacterial

CELLS

A typical bacterium
is about 1,000 times
smaller than an
animal cell, and can
only be seen in detail
with an electron
microscope. It has a
thick cell wall, but does
not have a nucleus. Bacteria
live either by using energy from
chemicals or sunlight, or by
absorbing food substances. Bacteria
can absorb food from dead matter,
such as plant and animal remains,
or from living cells.

BUBONIC PIAGUE

Before antibiotics were invented, bacterial
diseases sometimes swept vast areas in terrifying
epidemics. During the 13th and 17th centuries,
the bubonic plague, known as the Black Death,
killed millions of people in Europe. Bubonic
plague is caused by a bacterium that
lives in rats, and which is spread to
humans by fleas.

A spirillum has a
corkscrew shape.
Some form chains.

MAKING WASTE SAFE

Bacteria play an important part in processing our body
waste and in preventing it from causing pollution. In a
sewage farm, liquid waste is slowly trickled through beds
of clinker (lumps of solid ash) or fine gravel. Bacteria
living on the surface of the clinker digest the waste,
breaking it down into simpler substances. These can be
released into streams and rivers without harming wildlife.

TOOTH DECAY

We all have many kinds of bacteria
living on and in our bodies. Your
mouth contains bacteria that digest
traces of leftover food. If you do not
brush your teeth regularly, these
bacteria build up, forming a white
coating called plaque. Acids
produced by the bacteria attack the
hard outer covering of teeth. If the
acid gets through to the soft layer
underneath, the teeth decay more.

is a rod¬
shaped bacterium.
Bacilli live singly
or in chains.

A coccus has a
round cell. Some
cocci live in clusters
or in long chains.

BACTERIAL REPRODUCTION
Bacteria reproduce mainly by
dividing in two. With good
conditions - warmth, moisture,
and f ood - they do this every 20
minutes. This means that three
generations of bacteria can be
produced within just one hour. In
24 hours, repeated divisions would
produce nearly 5,000 billion
billion offspring!

Bacteria on
of tooth

313

LIVING THINGS

SINGLE-CELLED ORGANISMS

Wet PLACES such as the sea, ponds, or damp ground, are
alive with tiny single-celled organisms called protists. Although
protists are bigger than bacteria, most are still far too small to
see with the naked eye. Each protist cell is quite different from
those of bacteria. It contains a nucleus, and also has special
structures called organelles that carry out various tasks to keep
the cell alive. Protists feed in two ways. Some make their food
like plants - by using the energy in sunlight. Others, called
protozoa (“first animals”), catch and eat prey. But protists
cannot always be separated neatly into plant-like or animal-like
forms. Some can do both: they can make food
using sunlight and eat other organisms.

Il s

Liquid cytoplasm flows
through the pseudopods,
carrying organelles with it.

An amoeba’s top speed
is about 2 cm (just under
1 inch) in an hour.

: * p

Amoeba

An amoeba is a special kind of
protist that does not have a
fixed shape. Its single bag¬
like cell moves by flowing in
any direction. Amoebas live
in water, and feed by
engulfing their prey. Their
food becomes locked up in
bubbles called food vacuoles, where
it is eventually digested. To
reproduce, an amoeba simply
divides itself in two.

The nucleus controls how
the cell works. When the
amoeba reproduces,
both nucleus and •
cell divide in two.

The amoeba sends
out pseudopods in the
direction of motion.

Pseudopod

HOW AN AMOEBA MOVES
An amoeba can change parts
of its cytoplasm (cell fluid)
into a jelly-like solid and back
to a fluid again. It does this to
make temporary “feet”, called
pseudopods. As the amoeba
moves, the sides of the
pseudopods become solid and
stay still, while the front and
inside flow forwards.

As • <4?

.... yc.;

l .. • . •

Liquid cytoplasm
Jelly-like cytoplasm

: •

Food vacuoles digest
things that the amoeba
has engulfed. Any
remains are then ejected
from the cell.

An infected mosquito has Plasmodium cells
its salivary glands. These can enter
^fto^^ihuman when the mosquito /
J bites. /

A Didinium swims
about looking
for food.

The contractile vacuole is
like a pump. It collects
surplus water and then
squirts it out of the cell.

The Didinium has bumped into a
Paramecium. 77?e Didinium
stretches wide to take in its
enormous meal. Within two or three
hours, it will be ready to feed again.

PROTIST BATTLE
Protists may be small, but their
world includes some ferocious
predators. Here, a protist called
Didinium is attacking another
called Paramecium. The battle begins
when Didinium fires poisonous threads at its
prey. Although much smaller than its meal, the
Didinium then swallows the Paramecium. Both
these protists are ciliates - organisms that “row”
through water by beating tiny hairs called cilia.

MOSQUITOES AND MALARIA
Malaria is a dangerous disease that is particularly
widespread in the tropics. It is caused by a protist
called Plasmodium. People catch malaria when they
are bitten by a mosquito carrying this protist. Once
inside a human, Plasmodium lives and reproduces
inside liver and red blood cells. Every few days, the
new protist cells break out of the red blood cells,
producing bouts of fever.

The blood cell is
destroyed as its
invaders
reproduce.

ROCK-MAKING PROTISTS
Foraminiferans (“hole-bearers”) are protists that
live in microscopic shells rich in calcium. Each
shell is covered with tiny holes through which
special “feet” project to gather food.
Foraminiferans live in huge numbers in the sea.
When they die, their shells pile up on the seabed.
Eventually, they turn into rocks such as the chalk
seen in these white cliffs.

1 Mosquito (Anopheles arabiensis)

Human red blood cell
infected with
Plasmodium.

Find out more

Bacteria p.313
Cells p.338
Photosynthesis p.340
Asexual reproduction p.366
Factfinder pp.420, 422

314

LIVING THINGS

FLAVOUR FROM FUNGI

Fungi

For MANYPEOPLE, a fungus is a mushroom or a toadstool. But
mushrooms and toadstools are just the visible parts of fungi. The
rest of a fungus is made up of a mass of tiny threads called hyphae,
which are usually hidden in the ground, or in organic matter such
as dead wood. Unlike green plants, fungi cannot make food by
capturing sunlight energy. Instead, they use their threads to absorb
chemicals that have already been made by other living things that
have died. Together with bacteria, fungi are important
decomposers. They break down the remains of dead plants and
animals, releasing chemicals that can be recycled. Fungi do not only
feed on dead matter. Some attack living plants and

Although some fungi are poisonous, many
harmless species are used to flavour food.
These cheeses have been infected with
Penicillium f ungus. It grows through the
cheese, giving it a special taste. ^

animals and often cause diseases

Fruiting body

Spores formed by
fertilization inside
fruiting body

FI Y AGARIC

The fly agari c{Amanita
muscaria ) is a poisonous fungus that
reproduces by forming toadstools. The
toadstool has flaps called gills that hang from its
cap. The gills make spores, which are like tiny
seeds. These spores are shed into the air, and if
one lands in a suitable place, it produces a new
mass of fungal threads.

The gills are separated by
narrow gaps so the spores
can fall downwards. Each
toadstool can release
millions of spores.

Life cycle of a typical fungus

Black mould (Cladosporium
cladosporiodes) c \
growing on

damp wall. \

SINGLE-CELLED FUNGI
Yeasts are microscopic single-
L celled fungi that reproduce
1 mainly by budding. They
feed on sugars, turning
■ them into alcohol or other
substances through a
f process called fermentation.

Yeasts are used to produce
alcoholic drinks and to make
bread rise.

The stalk is
made up of a
mass of
fungal
> threads

^ joined

It together.

FUNGI AROUND THE HOME
Many kinds of fungi grow on and around houses.
Cool, damp walls are often colonized by a mould
that forms black patches. Timbers in old houses
can be eaten away by dry rot (Serpula lacrimans ),
while mildews and rusts attack garden plants and
farm crops.

Yeast cells

(Saccharomyces cerevisiae)

SIR ALEXANDER
FLEMING

Scotsman

Alexander

Fleming (1881-

1955) studied

medicine. In 1928,

he noticed that a

dish of bacteria in

his laboratory had w

accidentally become

infected by a fungus. Fleming

saw that the fungus had killed

the bacteria near it, and he

isolated the substance that the

fungus produced. He called it

“penicillin” - the first antibiotic

drug. As a result of later

research, pencillin has saved

millions of lives.

POTATO FAMINE
In the middle of last century, a
fungus changed the course of
history. The fungus concerned was
potato blight (Phtyophthora
infestans ), which rots potato plants.
It ruined much of the potato crop
in Ireland for several years, and
forced thousands of starving people
to emigrate to North America.

Puffball (Lycoperdon
pyriforme )

Find out more

PUFFBALL

A puffball’s spores form
inside a round head that
i gradually dries out and
becomes a hollow
bag. If an animal or
a raindrop strikes
the bag, spores are
Lflrcv puf f ed out of a
hole in the top.

Bacteria p.313
Photosynthesis p.340
Feeding p.343

Asexual reproduction p.366
Cycles in the biosphere p.372
Wastes and recycling p.376
FactFinder pp.420, 422

315

LIVING THINGS

Plants without flowers

Plants are different from fungi

because they can make their own food using
chlorophyll, a green pigment in their leaves.
Plants evolved from organisms called algae, and
fall into two main groups: plants without flowers,
and plants with flowers. Plants without flowers
appeared more than 300 million years ago. They
included liverworts, mosses, and ferns, and some of
them reached great sizes. Today, plants without
flowers still exist, but those on land are often quite
small, and are usually tucked away in shady places.
Plants without flowers spread by shedding spores.
Many of them, such as ferns, exist as two different
kinds of plant. One kind, the sporophyte, makes
the spores. These then germinate to make a
second kind of plant, the prothallus, which
produces gametes (sex cells).

Fern plant fi
(Sporophyte)S0 A

A kelp does not have
true leaves. It has
pointed fronds.

Plant

LOOKALIKE

Giant kelp (Macrocystis
pyrifera) is a huge
seaweed that

grows in
the cool waters of f California.

It can be 200 m (650 ft) long, 'C
and forms underwater “forests” ^
that provide a home for many
animals, including fish and sea
otters. Although they look like
plants, seaweeds are usually
classified as protists. Unlike
other protists, seaweeds
consist of many cells that live
and work together. They do not
have flowers, and they reproduce
by spores instead of seeds.

Zygote ^
beneath
gametophyte

Fertilization^ Egg cet ^ ! ^etophytlf

Sperm cell

f Life cycle of a typical plant without flowers

Ferns
have
special
tissues
that carry
water
through
the
plant.

WEALTH OF Al .GAE

Plants almost certainly evolved
from protists called algae,
jt which live by photosynthesis.

m This photograph shows green

HL alga called Volvox, which is
BE made of a ball of cells set in
K jelly. There are over 20,000
W species of algae. They include
. microscopic forms, but also
seaweeds such as the giant kelp.

TREE-FERNS f

Tree-ferns are the tallest *
non-flowering plants on
land. They grow mainly in
the tropics, although some
are found in cooler places
such as New Zealand.

Instead of a
stem, kelp
has a tough
rubbery stipe.

Liverworts either
have flat ribbons, or
ribbons made of
pieces that look _
like leaves..

f LIVERWORTS

I Liverworts are closely
related to mosses.
They are low-growing
plants that look like
pieces of green
ribbon. As the plant
grows forwards, the
ribbon keeps dividing
W in two. Liverworts like
places that are very damp,
such as rocky hollows and the
banks of streams.

Colony ruptures to
release daughter colonies.

USES OF SEAWEED

You probably encounter seaweeds every day
without knowing it. Extracts from seaweeds are
often used to thicken ice-cream.
^ They are also used in soft

v drinks, glue, toothpastes - and
even

Giant kelp is clamped to
the sea bottom by a root-like
anchor called a holdfast.

explosives. Seaweeds
contain large amounts of useful
minerals. They are
\ sometimes harvested and
used to make fertilizer.

Find out more

Mosses are
Ip anchored
with r00t ' l ' ke ha irs
called rhizoids.

MOSSES

A clump of moss is made up of a number of
plants growing closely together. Mosses
release their spores from capsules held on
little stalks. You can sometimes see these
capsules if you look closely.

Cells p.338
Photosynthesis p.340
Transport in plants p.341
Cellular respiration p.346
Asexual reproduction p.366
Sexual reproduction p.367
Fact finder p.420

Carrageenan and alginate
from seaweeds are used as
thickeners in foods.

316

LIVING THINGS

Conifers

YOU WILL NEVER SEE a conifer with flowers, and
it does not grow from spores. So how does a conifer
reproduce? The answer is that it forms cones. Each
cone makes either male or female cells, and the male
cells are carried to the female ones to produce seeds.
Conifers were among the first plants to make seeds.
Unlike spores, these seeds are complete with their ^
own food supply. There are about 550 species of
conifer, and nearly all of them are trees, such as
firs and pines. Most have narrow, tough leaves "-.jgg
known as scales or needles, and many are good
at coping with severe cold. In parts of the world
that have hard winters, conifers can form forests
that stretch from one horizon to another.

Each soft male
cone sheds
- millions of pollen
'.r grains (male cells)
r ■ into the air.

MONKEY PUZZLE
The Chile pine (Araucaria
auracana), also known as the
monkey puzzle, is an unusual
conifer that comes from South
America. It has sharp, leathery
leaves, and the male and female
cones grow on separate trees.

Scales close
in damp
l weather.

Young female cones sit
upright on the branches.
Their female cells are
fertilized by male pollen
grains that fall on them
from the air.

CONES AND SEEDS
Mature seed-bearing cones grow in many
shapes and sizes. Most are woody, but I
some are soft and look like berries. The I
cones of pines and spruces usually fall to I
the ground in one piece, but the cones fl
of cedars and firs slowly break up while I
still on the tree. M

Each scale
protects a
pair of
winged
seeds.

Pine Wm*
cone

scales open
in dry weather
to release the
seeds.

AMBER TRAP

9 /jjwjjF This spider is

millions of years
old. It has been
preserved in amber -
wm r the fossilized remains of
^ a sap called resin. Resin is

extremely sticky, and conifers use it
to stop small animals eating their
wood. If a conifer’s bark is wounded,
resin oozes out, trapping any insects
or spiders that it touches.

Mature

Kk female

1 ' cones hang
from the

■ branches. When

the winged seeds are
released, they flutter away.

Sitka spruce

The Sitka spruce (Picea
sitchensis) is a North
American conifer that
is now grown in
plantations all over the
world - both for its timber and for
making paper. The male and female
cones grow on the same tree. Spruces
are easy to recognize because their stiff
needles are attached to small pegs on the
branches. You can feel these pegs on an
old branch that has shed its leaves.

Adult
tree 1

Seed

inside

cone

Pollen

Ovule

Fertilization

Life cycle of a typical conifer

f-y ANCIENT
WL t f PINES

■"is The North

American
bristlecone pines
(Pinus longaeva) are the
world’s oldest living trees. Some surviving
examples took root more than 6,000 years
ago! Scientists study the width of growth
rings in their wood to see how the world’s
climate has changed.

Vew(Taxus baccata) has
flat needles that grow on
opposite sides of the
stems.

Giant sequoia

(Sequoiadendron giganteum)
has tiny, scale-like leaves
that lie almost

flat against the - -

stems. V _

Scots pine (Pinus
sylvestris) has
narrow needles that
grow in pairs. ^

CONIFER LEAVES S

Most conifers have small, leathery leaves that
stay on the tree for a year or more. Not all
these leaves are needle-shaped. Many are
short and flat, and are known as scales. A few*
conifers shed their leaves in autumn. These A
include the larches (Larix species) and ai^oV
the swamp cypress (Taxodium distichum). AN

The needles of
the larch (Larix'
decidua) grow
in bunches.
They fall in ^
autumn.

Find out more

Changing climates p.
Flowering plants p.‘
Transport in plants p
Grow h and developmen
Temperate forests p.:
Factfinder pp. 420, 4

246

318
-.341
;t p.362
396

317

LIVING THINGS

Flowering plants

We ALL LOVE the beautiful shapes, colours, and
scents of flowers. But flowers have not evolved for
our pleasure. They have developed as a way of
spreading pollen (male cells) to other flowers of
their own kind. Flowers receive pollen so that their
own ovules (female egg cells) can be fertilized.
There are more than 250,000 species of flowering
plant on Earth, and these are divided into two main
groups: monocotyledons and dicotyledons.
Monocotyledons have one cotyledon (a special leaf
packed inside the seed), and long adult leaves with
parallel veins. Dicotyledons have two cotyledons and
adult leaves with a branching network of veins.

Cucumber plant

Pollen from other flowers is
collected by the stigma. A
poppy flower cannot
fertilize itself with its
own pollen. i

Pollen is - — jgjj
produced
by the
anthers.

Insect
visitors eat
some of the
pollen, and
carry the rest to
other flowers.

Male flower

m Flower buds are
protected by two
S scales called sepals,
f ~ These fall off as the
flower opens. Each
common poppy flower
lasts for one day.

Bright petals
attract bees,
beetles, and
flies to the
poppy flower.

WIND

t/ POLLINATION
Grasses are
pollinated by
the wind. Their
anthers dangle
in the air so
that the pollen is
blown away. Grasses
make up one of the
largest families of
monocotyledon plants.

SEPARATE SEXES
Unlike the poppy flower,
which contains both male
J and female parts, the

cucumber plant (Cucumis
sativus) has separate male
and female flowers. Kiwi fruit
plants (Actinidia chinensis) are
either male or female.

Female flower
with long ovary

TREES AND FLOWERS
A tree is a plant with a
single tall, woody stem.
Some trees are conifers.
Hundreds of others are
broadleaved (flowering)
plants. Cherry trees
belong to the rose family
of flowering plants.

The poppy is a
dicotyledon, and has net-
veined leaves. Like many
dicotyledons, it also has
four petals.

Common poppy

The common poppy
(Papaver rhoeas) is a typical
annual flowering plant. It
flowers, sets seed, and dies
in a single season. Annual
plants grow rapidly, and are
quick to make use of any
patch of bare ground. Once
the seeds are scattered, they
remain dormant (inactive)
until conditions are right
for germination. This can
sometimes take several
years. Perennial plants live
for more than one season.
They have well-developed
roots, and often store food
underground in bulbs or
tubers. Some perennials
flower just once, but most
flower every year.

Flowering cherry tree (Prunus serrulata)

PARASITIC PLANTS

Some plants get all or part of their
food by stealing it from others. The
roots of mistletoe (Viscum allmm)
penetrate the wood on trees, and
take water and mineral salts from
the tree. But because mistletoe has
green leaves, it can also make its
own food from sunlight.

The Rafflesia plant,
f the giant flower
% A of which

is shown on
the opposite
page, is
completely
' parasitic.

Yellow, disc florets
produce pollen
and egg cells.

Ray florets

MANY FLOWERS IN ONE
A daisy {Beilis perennis ) is not a single flower.
The flowerhead is made of many tiny flowers
called florets, packed together. It is a
composite flower. The disc florets in the middle
are yellow and tubular. The ray florets around
the edge have a single white petal each.

318

LIVING THINGS

Insect pollination

Compared to a poppy, a foxglove (Digitalis
purpurea) has quite complicated flowers. The
petals are joined together to form a tube, and the
male and female parts of the flower lie under the
tube’s roof. This shape has evolved so that one
kind of insect, a bumblebee, can pollinate the
flower. The anthers and stigma in each flower
mature at different times, so a foxglove cannot
pollinate itself. When a bumblebee enters the
flower, it either collects pollen off the ripe male
anther, or brushes pollen from another flower
onto the ripe female stigma. When
the bee visits another flower, the
process is repeated.

As the bee
brushes against
the female stigma,
some of the male
pollen on its back is
left behind.

Foxglove
flowers grow in tall
columns. The lowest
flowers open first. The
male anthers mature first,
followed by the female stigma.

® Pollen

Ovule

The lower lip of
the flower acts as
a landing platform
for bumblebees.

^ The bee crawls
forwards to reach
nectar at the end of the tube.

Fertilization

Life cycle of a typical flowering

FLORAL GIANT
The parasitic Rafflesia plant of
Southeast Asia lives on the roots
of vines. Its flowers, which can
measure as much as 1 m (3 ft)
across, are the heaviest in the
world. They give off a powerful
smell of rotting meat to attract
pollinating flies.

Pollen grain containing
male nuclei r .

on stigma. _

Sharp spines of^
this Colts foot
(Tussi lago
farfara) pollen
get caught in
insects’ fur.

complicated

_ pattern of

projections and
hollows, which varies
according to the species of plant. Pollen grains
that are spread by the wind sometimes have
tiny “sails” to keep them airborne.

Male nucleus
travels down
pollen tube.

/ Pollen tube growing
downwards

SCATTERING SEEDS

Plants cannot move, but
they have evolved
unusual ways of
spreading their seeds far
and wide. The seeds of
the primrose (Primula
vulgaris) have special
food-bodies called
elaiosomes attached to
them. Ants eat these
food-bodies and
“plant” the seeds by
discarding them.

(Tarsipes rostratus)
ANIMAL POLLINATION
The pocket-sized honey possum of
western Australia (Tarsipes
rostratus ) lives entirely on nectar
and pollen. It feeds with a long,
brush-like tongue that reaches
deep into flowers. As it feeds, the
anthers brush pollen onto its fur,
while the stigma collects pollen
from other flowers. The flowers of
many kinds of tropical tree are
pollinated by bats.

Ovule

Female
nuclei inside
ovule

Find out more

M P"“~ FERTILIZATION
Before a seed can be
made, nuclei from male and
female cells have to join together. When a
pollen grain lands on the stigma of a flower of
the same species, the grain grows a fine tube
that makes its way through the stigma and style
until it meets an ovule. Male nuclei from the
pollen grain then combine with the female
nuclei in the ovule, and fertilization occurs.

Cells p.338
Photosynthesis p.340
Transport in plants p.341
Growth and development
p.362

Sexual reproduction p.367
Factfinder pp.420, 422

Ants carrying
away primrose
seeds.

319

LIVING THINGS

JELLYFISH, SEA ANEMONES, AND SPONGES are all invertebrates
(without a backbone). Invertebrates make up about 97 per cent of the
animal species on Earth. They have evolved a great range of body
forms, and many different ways of feeding and reproducing. Many
invertebrates live in water. Some spend their adult lives swimming or 1
drifting with the current, while others stay anchored to one spot.
Bryozoans (moss-like animals) and sponges filter food from the water.
Jellyfish, sea anemones, and corals - which

, .' r • 1 11 1 1 Float is a single,

belong to a group of animals called the -. gas-medpolyp j

rm/lo m n c o Ho/']/ llinir fV, r\ rt until that dCtS like i

Larva

The

jfjk'v^Wtj'X man-o’-war

■' ,■■ 1/ '1 1 (Physalia

f I f ! physalia) is a

< I / ( \Ly typical cnidarian.

p 0^0 'iSS Cnidarians

The blue, bag-like
Ip $ h* float of the man-o ’-

y/y war spells danger for sea
$p|%5frs animals, and for any

If swimmer that ventures too
close. A true jellyfish is a single
jj Jr animal that moves through the
water with a pulsating motion.
^ But a man-o’-war is a floating colony
of many animals called polyps, which
live and work together. Some of these
polyps form long tentacles that sting prey
and haul it in. Some specialize in digesting
food, while other polyps take care of
reproduction.

i a Sea anemones live

wUBmWum.MM ~ singly or in small

groups.

Medusa

SPONGES

Do you realize that some bath
sponges were once living animals in
the sea? A living sponge is lined
with special cells that work like
pumps. Water flows in through the
holes in the sponge, and out
through a vent. Any food in the
water is trapped by tiny sieves and
then absorbed.

Fertilization
outside body

Life cycle of a typical cnidarian

The man-o'-war's tentacles reach
up to 20 m (65 ft) when they are
fully extended. If a tentacle
catches a fish , it contracts and
pulls the food upwards.

HOW A JELLYFISH STINGS

The tentacles of a jellyfish are covered
with special cells that contain tightly
coiled stinging threads called nematocysts.
If a passing animal brushes one of these
cells, the nematocysts explode outwards.
Within a fraction of a second, the threads
turn inside out and stab the victim with
their sharp tips. Most nematocysts inject a
poison, but some wrap themselves around
the prey to prevent it escaping.

Nematocyst
f explodes outwards.

CORALS

Some corals live on their own.
Others grow in large colonies and
very slowly build up, layer upon
layer, to make coral reefs. A coral
usually feeds at night. It catches
food particles with its tentacles and
pulls them into its digestive cavity.

Out of water

Under water

SEA ANEMONES

If you explore a rocky shore at

low tide, you may sometimes find

small, jelly-like blobs attached to rocks . These

are probably sea anemones. A sea anemone

grips the rock with a sucker-like disc. When it is

underwater, it spreads out its ring of tentacles to

catch passing animals, which it attacks with

nematocysts (stinging threads). As the tide goes

out, the anemone withdraws its tentacles to

Find out more

Living things p.305
Growth and development p.362
Asexual reproduction p 366
Sexual Reproduction p.367
Seashores p.385
Fa ct Finder p. 420

Nematocyst
coiled inside cell.

Jellyfish, anemones, and corals

prevent them from drying out.

320

LIVING THINGS

If YOU WALK on a beach at
low tide, you may notice
coils of muddy sand that
look like toothpaste squirted out
of a tube. These are the feeding
remains of lugworms, which are
hidden beneath the surface.
Lugworms are animals that have a
long body divided into many sections.
Like earthworms and leeches, they
are members of a group of animals
called the annelids (segmented
worms). Annelids make up a small
fraction of the animals we call worms,
all of which are invertebrates. Two
other large groups of worms, the
platyhelminths (flatworms) and
nematodes (roundworms), do not
have segmented bodies. Many of
these worms live as parasites, feeding
inside other animals. Parasitic worms
are common in wild animals, but they
also infest farm animals and pets.
Some cause diseases in humans, such
as river blindness and elephantiasis.-

Detail of
tapeworm’s head

Hooks

Larva

Eggs

Fertilization
outside body

Life cycle of a typical annelid worm

Annelids that live on land usually

develop inside the egg, and hatch as fc jl

fully formed worms.

Annelids

A lugworm (Arenicola

maritima) is a segmented

worm that spends most of its

life in a U-shaped burrow

that it digs in muddy sand. It g Jn

lines this with mucus to

prevent it from collapsing,

and feeds by pumping water |

through the burrow. The §

worm swallows particles that 1||H

are carried in by the water,

and digests any organic

matter that they contain.

From time to time, it reverses
up the burrow until its tail meets ^@|§
the surface, where it ejects waste
sand and mud. It is this waste
matter that forms a cast on the surface,

PLATYHELMINTHS
The flat body of a
tapeworm is like a long w

egg-making machine. \
The worm lives in the
intestines of animals f

called hosts, such as cats \

and dogs, and hangs on I

by the suckers and hooks
on its head. The tapeworm
absorbs food from its host,
and releases eggs in packets
which break off from its body.

Earthworms help to keep soil
fertile. As they burrow, they
mix the soil layers and allow
air and water to soak in.

GIANT EARTHWORM
Australia is the home of the giant
earthworm (Megascolides australis ),
which can reach a length of over 3 m jd®
(10 ft). These worms live in the
same way as their smaller relatives - wjm
by swallowing soil and digesting the JBH
organic matter it contains,

LEECH TREATMENT

A leech has a segmented
body with a sucker at
either end. Many species
of leech feed on blood.
When a leech bites, it
produces a chemical that
stops blood clotting.
Leeches were once used
by doctors to drain blood
from patients.

SEA MOUSE
The segmented sea mouse
{Aphrodite aculeata) is a very
r unwormlike worm. It is about the
size of an adult’s hand, and has a
broad, flat body fringed with bristles.

Sea mice burrow through mud and
sand on the seabed, eating any small
animals they find on the way.

A leech can rapidly take in three or four
| times its own weight in blood.

RIFTIA WORMS
Giant riftia worms like
these were only seen for
the first time in 1977.
They live around vents
on the seabed, where
volcanically heated
water gushes out of the
Earth’s crust. The
worms contain bacteria
thatobtain energy from
chemicals in the water.

^ NEMATODES
I Roundworms live either as

parasites or as independent
animals. They are often
Wj$‘ hidden away, and exist in vast
numbers in soil and in plants.
yr Biologists often say that if all
the trees in a forest were taken
away, but the roundworms from the
trees left behind, you would still be
able to see the outline of the forest.

Find out more

Skeletons p.352
Nerves p.360

Growth and development p.363
Sexual reproduction p.367
Oceans p.386
Fact Finder p.420

Human

roundworms (Ascaris
lumbricoides)

321

LIVING THINGS

Arthropods

The LARGEST GROUP of invertebrates is made up of
arthropods - animals that have a segmented body and
an exoskeleton (hard case on the outside). This case
has special hinges that bend so that its owner can
move. As an arthropod grows, it moults (sheds its
, case) from time to time so that its body

Giant spider crabs live on
the seabed. Their body
cases are reinforced with
calcium, making them
hard and very strong.

can

expand. Well over a million species of arthropods
are known to biologists, making this the largest
group of animal species on Earth. Of these species,
nearly 90 per cent are insects. The remainder of
arthropods are either arachnids (mainly spiders),
crustaceans - such as crabs and lobsters - or
diplopods (millipedes) and chilopods (centipedes).

Adult

— Arthropods do
not have internal
skeletons.

Life cycle of a typical crustacean

Larva

Crustaceans

Most crustaceans live
in the sea. Sea-living
crustaceans can grow bigger
than arthropods that live on
land because their big body cases are
supported by the water. The largest
crustaceans of all are spider crabs (Macrocheira
kaempferi ), which can measure up to 3.5 m
(11 ft) with their legs stretched out. But not
all crustaceans are as big as this. The water
fleas that live in fresh water are also
crustaceans, but they are about the size of a
full-stop. A few crustaceans, including
woodlice, live on land and breathe air, but
they usually need damp conditions. J

The centipede’s first pair
of legs are modified to
act as a pair of
poisonous fangs.

Fertilization
outside body

if you look more closely, it is easy
to tell them apart. A centipede
has just one pair of legs on each
body segment, while a millipede
has two. Centipedes are hunters.

They paralyse their prey with
poisonous fangs. Millipedes live on
decaying plants. Both animals
prefer dark, moist areas.

A millipede’s
body is made up
of many ring-
shaped segments.
Each segment has
two pairs of legs.

SCORPIONS

Some arachnids look after their young until they can
■xF fend for themselves. A female scorpion gives birth to

fully formed young. The tiny scorpions climb onto their
mother’s back, where they are protected by the poisonous
sting in her tail. After they have shed their skin for the first
time, the young scorpions climb down from their perch.

The bolas \ .

spider hunts \ \

with a glue- \ H i

tipped thread X. J

instead of a web.

Arachnids

Spiders, scorpions, ticks, and mites
make up a group of arthropods
called the arachnids. Nearly all
arachnids live on land, and most of
them are hunters. Bolas spiders
hunt by whirling a silk thread tipped

SPINNING A WEB

A spider builds its web out of silk,
which is rich in protein. The silk is
formed by special glands in the
spider’s abdomen, and is squeezed
out through tiny nozzles called
spinnerets. The liquid silk solidifies
when it meets the air. An orb

A spider begins its web
by stretching strands of
silk between solid

The spider spins round
and round in a spiral until
the web is finished. The

with glue around in the air. If the
glue sticks to a passing insect, the
spider pulls it in.

supports. It climbs along web is covered with blobs
the silk using the hooks of glue that trap insects,
and bristles on its feet.

(round) web like this one can take
up to an hour to make.

322

chew wood into pulp for
making the nest.

LIVING

Adult'

** m

Head

Thorax

Insects

Insects have been very successful on land, mainly
because they have evolved the ability to fly. Insects with
wings can travel larger distances than wingless insects,
and so can find more food. A wasp is a typical flying
insect. Its body is divided into three sections - the head,
thorax, and abdomen.

It also has two pairs of \

wings. Like beetles and X. antennae (feelers). The

butterflies, a wasp mouthparts cut up food, and

undergoes a complete
metamorphosis (change in
shape). Young wasps are raised in
a nest by adults, but the young of
most insects must fend for
themselves. Insect parents and young
often live in different habitats. An
adult dragonfly lives in air, but a
young dragonfly lives in water.

Some insects spend their
whole life in water.

Each nest contains a single queen
wasp who lays eggs. The other wasps
are her offspring. They collect
food and look after the
eggs and young.

Hind wings of wasps
and bees are attached to the
forewings by tiny hooks.

Abdomen

Larva

Egg cell ® N Sperm cell

\ i

Fertilization
inside body

This life cycle is
typical of insects
that undergo
complete
metamorphosis.

Eggs

WINGLESS INSECTS
Despite its name, the silverfish is not a
fish at all, but a small, wingless insect.
There are about 300 species of silverfish.
Like other wingless insects, silverfish feed
mainly on dead plants. They sometimes
live indoors, where they eat lef tover food.

Life cycle of a typical insect

INSECTICIDES

Some insects are very useful because
they pollinate flowering plants. But
others are voracious plant eaters
that cause tremendous damage to
crops. Farmers often spray fields
with insecticides to prevent insect
damage. Unfortunately, these
chemicals often kill helpful insects
as well as the harmful ones.

BOMBARDIER BEETLE
The insect world is full of
animals that have unusual
ways of repelling attackers.
If a bombardier beetle is
threatened, it tucks up its
abdomen and mixes
together a brew of special
chemicals. These react with
each other and explode out of
the beetle, giving the attacker
a hot, poisonous shower.

Legs look
like stems

MANTIS ATTACK

A praying mantis relies on stealth and
camouflage. A hunting mantis flutters onto a
plant and folds up its wings. It then waits. If
another insect comes within striking range,
the mantis stabs it with its front legs. The legs
have sharp spines that grip the insect so that
it cannot escape the jaws of its predator.

JEAN-HENRI FABRE

Fabre (1823-1915) was a French
entomologist (scientist who
studies insects). He
researched insect life
extensively, and described
his work in a series of books.
Fabre’s observations, and his
gift for writing and painting,
helped to create great interest
in the insect world.

Sharp spines on
the legs grip the
trapped insect.

Find out more

Vision p.204

FLOWKRING PLANTS P.318
Blood p.348

Growth and development p.362
Skeletons p.352
Movement p.356
Sexual reproduction p.367
FactFinder pp.420,422

LIVING THINGS

Common octopus (Octopus vulgaris)

INTELLIGENT MOLLUSC

Octopuses have good eyesight
and large brains. They are
probably the most intelligent of
all invertebrate animals. They
can remember shapes and
colours, and are able to work out
quickly how to reach food. Like
squids, octopuses can move fast
by squirting a jet of water
backwards through a funnel.

MOLLUSCS

MOLLUSCS MAKE UP the second-largest group of invertebrates.
There are more than 90,000 species of mollusc, most of which live in
water, although some live on land and breathe air. All molluscs have a
soft body, which is often protected by a hard shell. There are three
main groups of molluscs. Gastropods, which include limpets, snails,
and whelks, usually have a coiled or pyramid-shaped shell. Bivalves,
such as clams and mussels, have a shell that is made of two parts joined
by a hinge. Slugs are gastropod molluscs, but they usually do not have
shells. The third group, cephalopods, which includes octopuses and

squids, have a small shell that is hidden
inside their bodies.

MATING SLUGS
These two slugs are
mating as they hang f rom
a thread of mucus. Each
slug is hermaphrodite
(both male and female).

When slugs mate, they
exchange sperm through
special organs, and each
slug then lays eggs. Being
hermaphrodite is not
unusual in the mollusc
world. Some molluscs
even start life as one sex,
and then change to
another.

Large, muscular foot

Gastropods

The common whelk (Buccinium undatum) is a typical gastropod
(“stomach-foot”) mollusc. It has a large, muscular foot and a shell that
coils in a clockwise direction. Only a few gastropod shells coil in the
other direction. The whelk’s shell is made by a special body layer called
the mantle. The whelk lives underwater, and breathes
using gills. The siphon on top of its head funnels water
into the chamber that contains the gills.

Land snails have
internal fertilization.
Their young develop
inside the egg and hatch
as miniature snails.

Cephalopods

Giant squids are the largest
cephalopod molluscs. They
are also the largest inverte¬
brate animals. Giant squids
live in the depths of the sea,
where they catch their prey
with sucker-covered
tentacles. There are many
stories about giant squids,
but little is really known
about them. The largest
specimens found measure
over 15 m (50 ft).

Adult

Larva

Egg cell

(ST®

Sperm
cell

Fertilization
Eggs outside body

Life cycle of a typical mollusc

KILLER CONE
Cone shells are
gastropods that attack
their prey with a
deadly poison. If an
animal comes within

range, the cone flicks
out its proboscis (tubular mouthpart). This stabs the victim
like a harpoon, and injects a paralysing poison. The poison
of some cones is powerful enough to kill humans.

Shell coils
in clockwise
direction.

Great slug (Umax
maximus)

Common mussel
(Mytilus
edulis)

Bivalves

Mussels spend most of
their lives anchored to
rocks by very tough byssus
threads. Like most bivalves,
they pump water through
their gills and feed on the
small food particles that
become trapped as the
water flows past. Some
bivalves can burrow and
move about. A few - like the
scallop - can even swim.

Find out more

Growti

Sexu^

Skeletons p.352
Movement p.356
Brains p.361

I AND DEVELOPMEN

lL reproduction
Fact finder p . 420

T p.362
p.367

324

LIVING THINGS

Starfish and sea squirts

Starfish AND THEIR RELATIVES, which include sea
urchins and sea cucumbers, make up a group of
invertebrate creatures called echinoderms (“spiny
skins”). Echinoderms are easy to recognize because
their bodies are built around the number five. A
starfish, for example, usually has five arms. It has five
sets of reproductive organs, and a digestive system that is
divided into five branches. All echinoderms have a
skeleton made of chalky plates. Sea squirts belong to a
different group of animals, the tunicates. They have soft,
bag-like bodies and tadpole-shaped larvae.

If a starfish loses
an arm, it
regenerates
(grows
back),

\ Tips of
P tentacles are
r“ sensitive to
light. This helps
the starfish to find
shady crevices in
which to shelter.

tube feet

• The underside of a

starfish’s arms carry two
rows of water-filled tube feet
connected by a system of
internal canals. Each tube foot
ends in a sucker, and can be moved
independently. The starfish uses
its tube feet to move and to
hold its prey.

Larva

W Echinoderms m

Like all echinoderms, starfish *9
have a skeleton made of chalky plates 9
covered by a thin layer of cells. The 9
plates have small bumps and spines, ^
and also tiny pincers that stop small
animals settling on the starfish’s body.

The plates are hinged to allow the
starfish to bend. A starfish’s mouth is on
the underside of its body. When it feeds,
the starfish pushes its stomach out
through its mouth, turning it inside out.

Fertilization
outside the body

Life cycle of a typical echinoderm

Water f Water sucked

expelled ' ^ in here

here / /

Shallow
water starfish

m starfish shapes

There are about
2,000 species of
ordinary starfish. Like
all echinoderms, they live only in sea
water. The starfish of shores and shallow
water feed mainly on living animals. They
use their tube feet to prise open the shells
of bivalve molluscs, and f eed by pushing
their stomachs between the shell halves.
Brittlestars and featherstars live in deeper
water. They use their long tube feet to
collect tiny particles of f ood, which they
then push to their central mouth.

Larvae have a
notochord - a
structure that is
related to the
backbones of
vertebrate
\ animals.

Brittlestar

Tunicates -'

Adult sea squirts are small animals that filter
food from sea water. They live either singly
or in groups, usually attached to rocks. Their
larvae are free-swimming and look quite
different. They are shaped like tadpoles.

Crown-of-thoms

starfish

Featherstar

Cushion star

Tube feet project

. through holes. , , Sand dollars
live on the
/y seabed in

shallow
water, and
feed by

> - ' i , collecting

small edible
particles.

SAND DOLIARS

A sand dollar is a sea urchin that has short
spines and a very flattened test, making it
look like a biscuit or a large coin. When the
spines have rubbed off after death, you can
see an intricate pattern of holes where the
tube-feet once poked out.

Test (skeleton)

SEA URCHINS
Sea urchins look very different
from starfish, but underneath
^ their spines they also have a
w>ody divided into five similar
W parts. A sea urchin has a
grounded test (skeleton), with
a mouth on the underside. It
feeds by creeping over rocks,
scraping of f small plants and
animals with its five teeth.

Find out more

Growth and development
p.362

Sexual reproduction p.367
Seashores p.385
Oceans p.386
Fact finder p.420

325

LIVING THINGS

Fish

STRANGE ARMOURED ANIMALS called ostracoderms swam in the world’s seas
more than 400 million years ago. They did not have jaws or fins, but they did have
backbones, making them the first vertebrates (animals with a backbone) on
Earth. Today, their aquatic descendants - fish - live throughout the world’s seas,
lakes and rivers. Fish are exothermic (cold-blooded)- their

Single
dorsal
fin —

Spiral valve
/es intestine

Stomach

body temperature changes according to their
surroundings. The colder the surroundings,
the less active they are. There
are more than 21,000 species
of fish. Most have jaws. Their
bodies are streamlined and are
usually covered with scales.

Fish absorb dissolved oxygen
from water through gills.

Overlapping placoid scales

SHARK’S TEETH
A shark’s teeth are larger,
sharper versions of the scales
that cover its body. The teeth
grow on a non-stop production
line that starts at the back of the
jaw. Each tooth gradually swings
forwards until it reaches the front of
the mouth. If it breaks off, it is soon
replaced by the tooth behind it.

Cartilaginous fish

Sharks, rays, and skates have skeletons that
are made of cartilage (gristle) instead of
bone. There are about 700 species of
cartilaginous fish, and nearly all of them
are predators that live in salt water.
Cartilaginous fish have a streamlined
shape and paired fins. Their skin is covered
in placoid (tooth-like) scales that gives
them a rough texture.

Eggcase hooked
around seaweed

DOGFISH

Dogfish are small sharks
that live in shallow water.
The male mates with the
female, fertilizing her
eggs while they are
inside her body. The
female then lays her eggs
in leathery cases that
hook around seaweed.
The parent dogfish do
not guard the eggs.

Asymmetric (irregular) caudal
(tail) fin shape is a characteristic
feature of sharks.

Gill arch. As the shark
moves forwards, the
gills absorb oxygen
from the water.

Good sense
of smell
helps the
shark to find
its food.

large surface area I -

for absorbing food.

Wide jaws
armed with
- ’ many rows of

oil-filled
liver acts
as a float.

teeth.

INSIDE A SHARK

An adult lamprey has a mouth
that is ringed with hooks. It
clamps itself to another fish
and sucks its blood.

| AWLESS FISH

This group, which includes lampreys
and hagfish, has some features in
common with the very first fish. They
do not have jaws or paired fins, and
their gills have openings like
portholes, rather than slits. There are
only about 70 species of jawless fish.
Adult lampreys live parasitically on
other fish, while young lampreys
filter particles of food from water.

Most of a shark’s body is made up of the muscles that it uses
to swim. As in all vertebrates, these are arranged in blocks
called myotomes. Part of a shark’s intestine is coiled into a
spiral, which gives the short intestine a large surface area for
absorbing food. The shark’s large liver helps to keep it afloat.

FISH SPEEDS

Generally, the more streamlined a fish is, the faster it
swims. Most fish swim faster than humans, who have an
average speed of 6 km/h (4 mph) over a short distance.

Human 6 km/h

Salmon 17 km/h (10 mph)

Blue shark 64 km/h (40 mph)

Marlin 80 km/h (50 mph)

326

LIVING THINGS

Heart

Br _ Anal
- fin gives
the fish
stability.

EELS

Some eels look like snakes, but their fins and gills
show that they are fish. The green moray
(Gymnothoraxprasinus) is a typical eel. It lurks in
rocky hideouts and attacks passing animals with its
sharp teeth. Eels start life as tiny larvae that look
quite different from adults. It can take several years
for a larva to develop into an adult.

Bony fish

This trout, and all the other fish shown on this page,
belong to a group called the bony fish - the largest of
the three groups of fish. These fish have bony skeletons,
and a special gas-filled bag, called a swim bladder,
which works like an inbuilt float. Their bodies are
usually covered with cycloid (slippery, flat) scales, and
their gills are tucked away behind a flap called an
operculum. During the last 250 million years, bony fish
evolved an amazing variety of shapes and sizes.

Adult

(

o ^

Sperm

cell

Fertilization
outside body

Head covered by
bony plates

The trout’s mouth. J
can shoot open
suddenly to suck in
small animals.

The gills are covered by an
operculum. This can open and
close to help pump water over the
gills.

Slippery overlapping scales reduce
the friction between the moving fish
and the water.

Life cycle of a typical bony fish

Most cartilaginious fish have
internal fertilization. They lay
eggs, or give birth to live young.

Dorsal fin gives the
fish stability.

Fins are reinforced
by stiff rays. These
can be moved
independently,
allowing the
fish to change
direction.

FISH THAT FLY
A flying fish (Cypselums helerurus)
escapes its enemies by launching
itself into the air. It bursts through
the surf ace of the sea and glides as
far as 100 m (330 ft) before
splashing back into the sea. A
flying fish’s “wings” are very
enlarged fins. Some species glide
using one pair of fins, while others,
like this one, use two.

Bony fish have regular caudal fins.
The caudal fin pushes thg^
fish forwards.

Stomach

Pectoral fins for steering.

PORCUPINE FISH
The greatest danger
for most fish is from
other predator fish around them.
When threatened, the porcupine
fish (Diodon hystrix) protects itself
by gulping water. This makes it
swell up like a balloon, and its
spines stand up on end. Although it
can hardly swim when it is inflated, its
it almost impossible to
attack.

Bony fish
have long
intestines
without a
spiral valve.

The swim bladder is
a gas-filled bag. It
adjusts to give the
fish neutral
buoyancy, so that it
does not rise or sink.

Special sensors in the
lateral line (fluid-filled
tube on each side of the
body under the skin)
detect movement in the
water caused by currents
and other animals.

SEAHORSl
Many bony fish lay vast number
of eggs, but take no part in
looking after their young.

Seahorses are different. The female
lays a small number of eggs in a special
pouch on the male’s abdomen. The
male seahorse looks after the eggs until
they hatch, and continues to look after
the young seahorses. Although
seahorses lay fewer eggs, each one has a
better chance of survival.

Eels have paired
pectoral fins, but
no pelvic fins.

White’s seahorse
(Hippocampus whitei )

Red batfish
(Halieutaea stellata)

DEEP-SEA FISH

There is no light or plant life
at the bottom of the sea.

Everything that lives here has
to feed either on “leftovers”
that fall from above, or on
other animals. The batfishes
are among the strangest fish
of the seabed. They eat
invertebrates and small fish,
and shuffle fowards using
their fins.

Find out more

Breathing p.347
Circuiation P.349
Internal environment p.350
Skin p.354
Movement p.356
Senses p.358
Factfinder pp.420, 422

327

LIVING THINGS

Amphibians

Amphibians HAVE A SPECIAL PLACE in the evolution of life
on Earth. Their ancestors were the first vertebrates to emerge
from water and spend some of their time on land. Most of
today’s 4,000 species of amphibian still divide their time between
water and land, but in different ways. A few amphibians, such as
the axolotl, spend nearly all their lives in water, but most spend
their adult lives on land and return to water only to breed.
Amphibians do not usually have scales, and their skin is generally
loose-fitting and moist. All amphibians are exothermic (cold¬
blooded) and are divided into three groups: the anurans (frogs
and toads), the urodeles (newts and salamanders), and a small
third group without legs, the caecilians, or apoda.

FI.UNG FROGS

The flying frog

(Rhacophoms nigropalmatus) hunts for small
animals on trees in southeast Asia. To move

Large mouth
without teeth

Thin, moist skin
absorbs oxygen.

Eyes and nostrils are
above water when

rest of the body is
submerged.

Back legs
have five toes.

Anurans

Front legs have
- four toes.

from one tree to another, it launches itself into
the air. The frog spreads out its webbed feet-
which work like small parachutes - and angles
them to steer as it glides.

Adult

Tadpole ^

larva & ' ^1 Sperm cell

^3* Egg cell ®\

t i

Eggs

(spawn)

Fertilization
w outside body

Life cycle of a typical amphibian

Amphibians in this group have short bodies, strong legs, and
no tails. This South African bullfrog (Pyxicephalus adspersus) is
a powerful predator. It feeds on small mammals and reptiles,
and also on smaller frogs. Like all frogs, it has a thin skin that
has to be kept moist. Toads usually have drier skins, and are
usually covered with warts. On land, frogs usually move by
hopping, while toads often walk. Frogs and toads both have

simple, internal lungs.

Poison is secreted
by glands on the

frog’s skin POISON-ARROW FROGS

The thumb-sized poison-arrow frog (Phyllobates
tenibilis ) that lives in the forests of Central and South
America is one of the most dangerous of all
amphibians. The frog’s bright colours warn other
animals that its skin produces a deadly poison. Forest
Indians use this to make poison-tipped arrows that

kill other animals.

LOOKING AFTER EGGS
Most frogs and toads lay hundreds or
thousands of eggs, and then abandon them.
Other species lay fewer eggs, but look after
them more carefully. The male midwife toad
(Alytes obstetric am) wraps the female’s eggs
around his legs. When the tadpoles are ready
to hatch, he carries the eggs to water.

WATER-HOLDING FROG
Some frogs and toads survive
drought by burrowing
underground and sealing
themselves in a waterproof
membrane. The Australian
water-holding f rog ( Cyclorana
species) spends most of its
adult life underground. As soon
as it rains, the frog breaks out of
the membrane and digs its way to
the surface.

EARLIEST AMPHIBIAN

The oldest amphibian fossils that
have been discovered belong to a
creature called Ichthyostega , which
lived about 375 million years ago.
This animal was about 1 m (3 ft)
long. It had a streamlined, fish-like
body, but strong legs that supported
its weight on land.

Sturdy ribs
supported the
weight of internal
organs.

328

LIVING THINGS

r Urodeles

These amphibians have longer bodies and
smaller legs than anurans. Some have flattened
tails that they use for swimming. The fire
v salamander (Salamandra salamandra) has

bright colours for the same reason as the poison-
arrow frog - to warn that its skin is poisonous.
^ Newts and salamanders are found mainly in
the Northern Hemisphere, and they live in
water or in damp places, such as the woodland
floor. Fire salamanders mate on land. The^^
eggs develop and hatch inside the
mother’s body. — AwE

Unlike frogs and toads, newts
and salamanders do not lose
their tails as they grow up.

/ 3. After a

series of moves,
the male settles in
front of the female. When
the female touches his
tail, he deposits his
sperm packet. The
female drops down onto it
so that the sperm are
taken into her body.

Salamanders have
small tdes, and their feet
are not webbed.

Fire salamander’s
skin secretes a toxic
chemical.

2. The male then swims in front of the
female, and settles at right angles so
that he is blocking her way. The
male waves his tail, pumping his
scent towards the female.

1. The smooth newt’s underwater dance
begins when the male approaches the
female and touches her side-on. He is able
to smell "scent” chemicals that she releases
into the water.

Female

COURTSHIP DANCE

When newts or salamanders ••

mate, the male deposits

a packet of sperm and

the female picks it up. In the case of the

fire salamander, the male carries the

female and then lowers her onto his

sperm packet so that the sperm are taken

up into her body. The smooth newt

(Triturus vulgaris ), shown here,

mates underwater. The male

dances in front of his partner

before mating occurs.

Caecilians

Caecilians are aquatic or burrowing
animals that live in the tropics. They have
no legs, and their cylindrical shape makes
them look more like worms or small,
rubbery snakes than amphibians. But some
caecilians lay eggs that develop into
tadpoles with gills, linking
them directly to

salamanders and --

other amphibians.^^^%j|M|^g^SSM

Olm belongs to the
urodeles group.

AXOLOTL

The axolotl (Ambystoma mexicanum) is
sometimes called the “Peter Pan” of
the amphibian world because it never
g rows up. Axolotls are
salamanders that come
from one particular lake
in Mexico. Like many
salamanders, they begin life
as tadpoles with feathery gills.
^ Yx But i nstea d of losing their

gills and taking up life
wttL on l an d> axolotls

gp v usually stay in

water, and breed

changing shape.

Although
^ caecilians
have eyes, they
are nearly blind.

Most

caecilians have
a covering of
keratin plates.

Find out more

LIFE IN THE DARK

The deep limestone caves of southern Europe
are home to the olm (Proteus anguinus). This
aquatic relative of salamanders has a pencil-thin
body with tiny legs, and is almost completely
blind. Olms live in underground pools and
rivers, where they feed on small water animals.
A similar cave-dwelling salamander lives in the
caves of southern Texas, United States.

Circulation p.349
Internal enmronment p.350
Skin p.354
Muscles p.355
Brains p.361

Sexual reproduction p.367
FactFinder PP.420, 422

329

LIVING THINGS

Reptiles

The cobra’s hollow fangs are
positioned at the front of its mouth.
It can squirt venom through the
air towards an attacker.

There ARE ABOUT 6,500 SPECIES of reptile alive today.
Further back in time, there were many more. For about 200
million years, prehistoric reptiles dominated life on Earth, and
they included the largest plant eaters and predators ever to
live on land - the dinosaurs. Reptiles were the first vertebrates
to become properly adapted to life on land. They do not need
moist conditions in which to live. Their dry, scaly skin stops
them from losing too much body water and their eggs, which
they lay on land, have thick, leathery shells that stop them

drying out. Because reptiles are exothermic (cold-
blooded), they usually live in warm parts of the
world where the Sun warms their bodies and
.: ■ \ makes them active.

HMhkC (£ Like all reptiles, the boa is

exothermic. When cold, it

HKXfcL. gets too hot, it

y - ■: '/V

. the shade.

Flexible ligaments and joints
allow the two parts of the
lower jaw to move apart
during swallowing.

When threatened, the cobra
spreads out the ribs behind
its head.

Snakes sometimes have over 400
pairs of ribs, but usually just one
working lung. A snake’s kidneys lie
one behind the other so that they
fit into the narrow body. _

BOA CONSTRICTOR

A boa constrictor (Constrictor constrictor) kills its prey by
suffocating it. The snake coils its body around the victim,
preventing it from breathing. The snake waits until its prey is
completely dead before swallowing it head-first. Boas produce
eggs, but the mother snake keeps them in her body until
they are ready to hatch.

Squamates

Today’s reptiles are split into three
major groups. By far the largest
group is the squamates (snakes and
lizards). Although snakes look very
different from lizards, they probably
evolved from lizard-like ancestors by
gradually losing their legs. The
Indian cobra (Naja naja) is a typical
front-fanged snake. It kills its prey by
injecting a poison, and swallows its
food whole. Cobras lay about 20
leathery eggs, and the female guards
the eggs until they hatch.

Small,

overlapping

scales

GIANT LIZARDS

The Komodo dragon (Varanus komodensis) is
l the world’s largest lizard. An adult

can measure 3 m (nearly 10 ft) from
■Sir head to tail, and can weighmore than
ji toQ i a person. Komodo dragons live on
WF islands in Indonesia, and feed on
animals as large as deer.

Geckos have large eyes,
like many nocturnal
hunters. -

CLIMBING LIZARDS
Geckos are nocturnal
lizards that hunt
small insects. They
can run up walls,
and can even walk
upside-down on
ceilings. Geckos
are able to do this '
because they have
special pads on
their toes. These are
covered with tiny
bristles that hook 1
into small cracks A
on the surface
they are J

climbing. B

SHEDDING SKIN

Lizards and snakes shed the
outermost layer of their skin from
time to time so that they can grow.

This process often takes several
days to complete. The skin starts to
split around the head, and then
begins to peel away along the
^ rest of the body.
-M Snakes often
_ ri ^ jrak JR shed their skin
B in a single piece.

Marine iguana feeds
on algae growing on
submerged rocks.

DIVING LIZARD
The Galapagos Islands
in the eastern Pacific
arc the home of the
marine iguana
(Amblyrhynchus
cristatus), the only
lizard that feeds in the
sea. When a marine
iguana dives, its
heartbeat slows down.
This helps it to save
oxygen, and also
prevents too much of
the iguana’s blood
being chilled by the
cold water outside.

This slow worm
(Anguis fragilis)/s
shedding its skin in
very large pieces.

330

LIVING THINGS

The crocodile swims by holding
its legs close to its body, and
waving its flattened tail.

Although the
estuarine crocodile is
a fearsome predator,
it is a careful and
gentle parent.

Crocodilians

Crocodiles, together with their relatives the alligators,
caimans, and gavials, belong to a group of reptiles called
the crocodilians. Crocodiles look like giant lizards, but the
arrangement of bones in their skulls shows that they are
more closely related to dinosaurs than to any living reptile.
There are about 21 species of crocodilian, and all live
partly in water. The largest species, the estuarine or
saltwater crocodile (Crocodylus porosus ), can reach a length
of more than 6 m (nearly 20 ft), making it the biggest
reptile in the world.

A crocodile’s body is
covered with large
scales. The scales on the
back are reinforced with
bone to form armour
plating. ,

The crocodile’s nostrils are
at the tip of its snout. It can
close them when it dives.

Simple, peg- _
shaped teeth for
tearing flesh

A mother

crocodile carries

her young to water

in her mouth. She guards

them for several months until they

can fend for themselves.

Skull of estuarine
crocodile

Short,

powerful legs

Broad
snout -

Long-

narrow

snout

with

small,

sharp

teeth.

Life cycle of a typical reptile

REPTILE SKULLS

The estuarine crocodile’s skull is broad, and
its jaw muscles are extremely powerful. It
feeds on large animals, dragging its prey
underwater and tearing off pieces, which
it swallows whole. The smaller gavial
(Gavialisgangeticus ), which lives in rivers I

in the Indian subcontinent, eats fish. Its ^
skull has

Shelled

egg

The eggs of some reptiles
develop inside the body. The
young are born after hatching.

Fertilization inside the body

very narrow jaws, and it catches
its food by snapping like a bird.

TUATARA

Tuataras are the only living
descendants of the sphenodonts :f|| Ur
- a group of reptiles that were
common millions of years ago. ^

Unlike other reptiles, tuataras can
remain active in quite low temperatures.
Wild tuataras (Sphenodon punctatus ) live
under special protection on small
islands off New Zealand.

A fully grown tuatara is
about 60 cm (2 ft) long.
Tuataras live in burrows,
and feed on insects, eggs,
frogs, and young
seabirds.

RULING REPTILES

Reptiles were once the most successful
vertebrates on land. Dinosaurs ranged from
chicken-sized animals to the giant herbivore
Brachiosaurus. The dinosaurs, together with
many other forms of life, died out during a
mass extinction. Some scientists think this
was caused by the impact
of a giant meteorite. Thjs

dinosaur is
called
Deinonychus

Chelonians

Tortoises, turtles, and terrapins make
up a group of reptiles called chelonians.
These animals usually have a bony shell
covered in scales made of horn.
Chelonians feed on both plants and
small animals, and have horn-covered
jaws instead of teeth. This Galapagos
tortoise (Geochelone ** **maMmm

elephantopus) is a giant species that can
weigh as much as three people.

Find out more

Breathing p.347
Internal env ironment p.350
Skeletons p.352
Movement p.356
Senses p.358

Sexual reproduction p.367
FactFinder pp.420,422

331

LIVING THINGS

Birds

Fossil EVIDENCE SHOWS that birds have evolved from
reptiles. Like reptiles, birds are vertebrates that lay eggs with
shells, but they have some features that reptiles do not have.
Birds are the only animals that have feathers. They also have
wings and beaks. Birds are endothermic (warm-blooded); the
temperature of their body does not change with variations in
external temperatures. Because a bird’s body is warm, it is always
ready to fly into action. In fact, birds are the most powerful fliers
of all living things. There are about 9,000 species of bird. They
live everywhere: in city centres, tropical rainforests, and ice floes.

Bird design

During the course of evolution,
birds have developed bodies that
are light, streamlined, and
compact. This kingfisher (Alcedo
atthis) is about 16 cm (6 in) long,
but weighs just 40 g (1.5 oz). Like
all birds, it has feathers. Its feet are
covered in scales, and it has a hard
but lightweight beak. Small birds
like the kingfisher have the highest
body temperatures of all animals.
They need a constant supply of
food to keep their bodies working.

Life cycle of a
typical bird

Shelled

egg

Adult

Lungs are very efficient at
extracting oxygen
from the

Kidney

Sperm

cell

Stomach

Fertilization
inside body

BIRD SKELETON
The delicate skeleton of a
flying bird can make up as
little as five per cent of its total
body weight. Although the
wing bones are hollow, they
are reinforced by struts to give
them strength. The wing
muscles are anchored by a
bony flap, called a keel, which
sticks out from the breastbone.

Skull

Hollow wing
bones

Ankle

Heart

Liver

Gizzard

temporary food
store

INSIDE A BIRD
Birds do not
have teeth, and so
cannot chew their food. Instead,
hard food is ground up in a
special chamber called a gizzard.
A bird’s lungs are much more
complicated than those of
mammals or reptiles. When a
bird breathes in, the air flows
into special spaces called air sacs.
It then travels through the lungs,
and into more air sacs, before
being breathed out.

Feathers have
evolved from
reptilian scales.

Wings have
evolved from
reptile

FEATHER CARE
Feathers need constant care to
keep them in good condition.

Birds use their beak like a comb
to draw the barbs and barbules
together, and also to remove lice
and other parasites. Most birds
moult (shed) their old feathers
once or twice a year and grow a new
set. This duck is spreading a special
oil over its feathers, which will keep
them waterproof.

BIRDS WITHOUT WINGS
The brown kiwi {Apteryx australis)
from New Zealand is one of several
birds that have lost the ability to fly.
Its wings are tiny, and its feathers are
hair-like. Unusually for a bird, the
kiwi has a good sense of smell, which
it uses to find food.

Courtship plumes from a wild turkey
(Meleagris gallopavo). Each feather has
two flexible shafts and short barbs.

Flight feather has
strong shaft and tightly
locking barbs and
barbules.

Down feathers insulate
the body. The barbs do
not hook together, but
spread out to
form a fluffy layer
that traps air.

Body feathers
streamline the
body. The base of the
feather is soft and
fluffy, but the tip has
a flatter surface.

FEATHERS
Feathers are made of keratin, the
L same substance that our hair and
fingernails are made of. A quill
that carries lots of side-branches,
called barbs, runs down the
feather. The barbs have even smaller
branches, called barbules, which hook
together to form a single surf ace. A
bird’s plumage can contain over
10,000 feathers of several
different types.

Sail-shaped display feather
from a mandarin duck (Aix
galericulata) wing is used to
attract females.

LIVING THINGS

The Gouldian
finch

(Chloebia a
gouldiae)

has a ^

typical seed-
eater’s beak -
short, sharply
pointed, and
strong. The finch
uses it for cracking
open seed husks.

The female chaffinch incubates the
eggs. She has a special area of
bare skin, called a brood patch,
on her front. This allows her
body heat to warm A

the eggs.

Brightly coloured male
chaffinch does not share
the task of incubation. His
colours would make it
easier for a predator to
spot the nest. ^

The beak of the
greater flamingo
(Phoenicopterus
ruber) works
like a sieve.

The lower bill l
moves up and I
down to pump }
water against
the top bill,
where a fringe
of slits traps
the food.

Nest of eggs

A young bird develops outside
its mother’s body, inside an egg.

It is protected by a hard shell that ™

stops water escaping, but that allows oxygen in. Small birds
like this chaffinch (.Fringilla coelebs) lay several eggs in a
nest. The young birds do not develop unless the female
warms them by incubating them (sitting on them).

Nest chamber

The avocet (Recurvirostra
avosetta) is one of the few
birds that has an upturned beak. It
swings it from side to side to catch
small animals in water.

African weaver birds (Ploceus species) are
famous for their crafted nests. Each nest is
made by the male, who weaves blades of grass
with his beak and feet. When the nest is finished, he
hangs below it and flutters his wings to attract a female.

Parrots (Psittacidae M
family) live
almost entirely
on fruit and
seeds. A parrot
cracks open

the seeds with i ^
the base of its
powerful beak and
grasps fruit with the hook
at the tip.

Entrance

tube

Entrance

NESTS

-■ All birds lay eggs,

^ but not all make nests.

Some seabirds lay their eggs
W straight onto cliff ledges, and many ground-dwelling
birds lay eggs in a simple hollow, called a scrape, which
they line with feathers. Birds that build complicated nests
use many kinds of materials. These include leaves, sticks,
mud, hair, spider’s webs, and even saliva. A bird does not
have to learn how to make a nest - it docs it by instinct.

The rufous ovenbird
(Furnarius rufus) from
South America builds a
football-sized nest from
mud, which hardens as it
dries. The nest has a
curved corridor that leads
to an inner chamber.

The kestrel (Falco
tinnunculus) eats
insects and small
mammals. Like
other birds of
prey, it tears
up its food with L
its sharp, \

hooked beak.

V The A frican palm swift
f (Cypsiurus parvus) glues
feathers onto a palm leaf. It
then glues its eggs onto this mat
of feathers. The eggs stay
attached even in strong winds.

r BEAKS AND FOOD

A bird’s beak is made of bone
covered by a layer of horn. In an
adult bird, the bone usually stays
the same size, but the horn grows
continuously to allow for wear. A
beak is designed to suit the way its
owner feeds. Birds with specialized
feeding habits usually have
distinctive-looking beaks.

BIRD MIGRATION

Birds often spend summer and winter in
two different places. Many species
^ ^ of geese breed in the far

0 north, where food is

0 abundant during the
^ ^ brief summer. When

_ it becomes colder,
as winter begins,
0- they fly south. Their

long journeys are called
migrations.

CUCKOOS

The female cuckoo (Cuculus
canorus) does not make a nest.
Instead she lays an egg in another
bird nest while its owners are away.
When the young cuckoo hatches, it
pushes the other eggs out of the
nest. Its foster parents do not
realize that it is a cuckoo and work
non-stop to keep the imposter
supplied with food.

Find out more

ClRCUIATION P.349
Internal environment p.350
Skeletons p.352
Movement p.356
Brains p.361

Sexual reproduction p.367
Fact Finder pp.420, 422

333

LIVING THINGS

Mammals

shrews and bats to elephants and whales. All mammals
have three important features in common. They are
endothermic (warm-blooded), they have hair or fur, and
they suckle their young on milk produced by the
mother’s mammary glands. This milk is a complete food
that nourishes a young mammal until it is able to
find food for itself. On land, mammals - of AMM

which there are about 4,000 species - are
the most widespread vertebrates.

teeth cut through meat.

carnivore. Its
long, pointed
canine teeth
grip its
^ prey.

TEETH AND DIET

A mammal’s teeth are as varied as tools in a toolkit. Different
adult mammals eat many different kinds of food, and their
teeth are specially adapted to match their diets. Carnivores
(meat-eaters) have teeth that grip or slice. Herbivores (plant-
eaters) have some teeth that cut, and some that grind.
Omnivores, which live on all kinds of food, have teeth that can
grip, slice, cut, and grind. Some mammals,
including those that feed on ants,
and whales that feed on krill, have lost
their teeth altogether.

Fertilized egg
develops
inside body.

Milk for the foal is
produced by the mother’s
mammary glands.

Zebra’s body
is covered in
hair.

Fertilization inside body

Life cycle of a typical mammal

Common or plains zebra
(Equus burchelli)

ARMOURED MAMMAL
'The tree pangolin (Manis Lricuspis) from
tropical Africa is protected by hard, leaf-
shaped scales that cover most of its
body. It feeds on ants and termites,
which it catches with its long tongue.
Like the anteaters of South America,
pangolins do not have any teeth.

Placental mammals

The zebra, like all the mammals on this page, is a
placental mammal. A zebra foal develops inside
its mother in an organ called a uterus (womb).
The foal gets nourishment from its mother
through the placenta, a spongy tissue that passes
food from the mother’s blood to the baby’s
blood. The foal is well developed when it is born,

and is soon able to run.

As soon as a young
dolphin is born, adult
dolphins push it to
the surface so it can
take its first
breath.

AQUATIC MAMMALS
Dolphins are cetaceans - mammals
that spend their whole life in the
sea. During the course of evolution,
they have developed a streamlined,
fish-like shape, but they still breathe
air and suckle their young.

Common tree shrew
( Tupaiaglis )

Spinner dolphins
(Stenella longirostis)

k TREE SHREWS

The tree shrews of southern and eastern Asia may
resemble the first mammals that evolved from reptilian
ancestors. Tree shrews are nocturnal (active at
night). They have large eyes and a well-
^^^Hdeveloped sense of smell. Biologists believe that
I similar animals shared the Earth with the first
dinosaurs, over 200 million years ago.

FLYING MAMMALS
Bats make up a quarter of all
mammal species. Together with 9
insects and birds, they are the only ®
animals capable of powered flight.
Most bats live on insects, which they
pinpoint in mid-air by using pulses of
sound. Larger species eat fruit.

i w*

A rabbit is a herbivore. It
has front teeth that cut and
rear teeth that grind.

Scissor-like carnassial

A dog is a

If YOU ASK A FRIEND to name any animal, they will
probably name a mammal. We are mammals, and so too
are most of the large animals we see in daily life. But not
all mammals are large - they range in size from tiny

334

LIVING THINGS

Small front legs are
used for digging,
grooming and fighting

A young kangaroo, called a joey,
jumps into the pouch if danger
threatens. As it climbs aboard, it
doubles up so its head and feet
point in the same direction.

KOALA

The koala (Phascolarctos cimnreus) is an Australian
marsupial that has adapted to life in trees, and to
a diet that consists mainly of eucalyptus leaves.
Young koalas spend their early lives in their
mother’s pouch. When they are large enough,
they emerge from the pouch and cling to her
back. Despite their shape, koalas are not close
relatives of bears. Bears are placental mammals,
not marsupials.

VIRGINIA OPOSSUM
The Virginia opossum (Didelphis
virginiana) is a rare success story in
the marsupial world. This tree¬
dwelling North American species
has steadily increased its range,
and now lives as far north as
Canada. It has managed to do this
by adapting to lif e alongside
humans. It wanders into gardens
and over rooftops, and searches for
food in household waste.

Marsupial mammals

Marsupial young are born in
an immature state. After birth,
they crawl into their mother’s
marsupium (pouch) where
they develop. In kangaroos,
the marsupium is a roomy
In other marsupials, such as
quolls, it is little more than a
flap. The marsupium contains
teats, and the young animal
fastens itself onto a teat to
feed. There are about 260
species of marsupials.
Although people often
associate them with Australia,
many live in South America.

Fur or hair protects the skin
from the Sun and injury. It
also keeps body moisture
out and heat in.

A female kangaroo can raise
young on a production line
system - with one forming
inside her uterus, one in her
pouch, and another one almost
ready to live on its own.

Long, sharp nails for
shovelling sand.

UNDERGROUND MAMMAL
Many marsupials have evolved
shapes and ways of life that match those

of placental mammals. The marsupial mole (Notorycles typhlops) is
shaped very much like a placental mole, with a blunt body and powerful
digging legs. Like a placental mole, it also feeds on grubs and worms.

QUOLL

The beautifully spotted quoll (Dasyurus viverrinus) is Australia’s
marsupial equivalent of the cat. A nocturnal predator, it feeds on
small animals such as insects and smaller marsupials.
Unfortunately, the quoll is not such an efficient hunter as its
placental equivalent. Since the domestic cat was introduced into
Australia, quoll numbers have fallen. Many other marsupials have
also declined because of competition with placental mammals.

MONOTREMES

The duck-billed platypus
(0 mithorhynchus anatinus) is a most
bizarre mammal. It has webbed
feet, a beak like a bird, and it lays
eggs. When young platypuses hatch,
they feed on their mother’s milk,
which is produced from teatless
mammary glands. The young
animals lap the milk from her fur.

Only two other species of mammal - the spiny
anteaters - lay eggs. With the platypus, they make
up a tiny group of mammals called the monotrernes.

Find out more

Teeth and jaws p.344
Breathing p.347
Circuiation P.349
Internal environment p.350
Skeletons p.352
Sexual reproduction p.367
Fact Finder pp.420, 422

335

Arms are
very long

Fingernails instead of claws

Orang-utans grip branches
with their hands and their
feet. They can walk on two
legs, but they mostly
use all four.

We BELONG to a group of mammals called the
primates. Primate means “the first”, although there is
really no top place in the evolution of living things. The
primates are divided into two groups: the anthropoids
(humans, apes, and monkeys) and the prosimians (which
include lemurs, bushbabies, and aye-ayes). Humans are all
members of one species, Homo sapiens. We live on the ground
and walk on two legs, but most primates live in trees, and use
all four legs. Primates have forward-pointing eyes, which help
in judging distances, and flexible fingers and
toes that can grip branches. Anthropoids
have large brains and are highly intelligent.

Compared to an ape’s
skull, a human skull
has a very large brain-
case, short jaws, and
small teeth.

ORIGIN OF HOMO SAPIENS

The shape of the human skull is important in deciding
how the human species evolved, because it can be
compared directly with the fossilized skulls of our distant
relatives. Humans almost certainly evolved from ape-like
ancestors. Fossils show that several species of human-like
animals, called hominids, existed between one and five
million years ago. Today, only our species survives.

Orang-utans,
and all other
apes, have
no tail.

Orang-utan

Most primates live in the tropics
and subtropics. There are about
180 species altogether. The orang¬
utan (.Pongo pygmaeus) is a member
of the ape family, which also includes
gorillas and chimpanzees. Orang¬
utans live in the rainforests of southeast
Asia. Like many primates, they are under
threat because their forest home is being
cleared for timber and for farmland.

HUMAN SUCCESS
Humans are by f ar the most
numerous of all primates. In the
last 300 years, the human
population has grown from about
1,000 million to nearly 6,000
million. Never in the history of the
world has a single species had such
a wide-ranging effect on other
living things.

CHIMPANZEES
We often use tools to carry out
particular tasks. So, too, do some
other primates. Chimpanzees, for
example, use sharp sticks and
blades of grass to probe for food.
Baboons sometimes squash small
animals with stones. Several other
kinds of animal use tools, but they
do this mainly by instinct. Primates
can learn how to make tools by
watching each other at work.

PROSIMIAN PRIMATE

The aye-aye (Daubentonia madagascariensis ) is an
endangered prosimian that is found only on the
island of Madagascar in the Indian Ocean. It is a
nocturnal tree-dweller and feeds on insect grubs and
young leaves. The aye-aye’s front hands have extra
long third fingers, which it uses to pick out grubs
from bark crevices.

Chimpanzee (Pan troglodytes)
using tool to dig
out insects
from bark.

LOUIS AND MARY LEAKEY

The work of the Leakey family has helped to
piece together the story of how our species has
evolved. Louis Leakey (1903-72) discovered
hominid fossils in East Africa, and suggested
that humans originated in this region. His wife
Mary (1913-1996) has discovered
several fossils of human
ancestors and human
footprints that date
back nearly 3
million years.
Richard Leakey
(born 1944), their
son, has also made
several important
fossil finds.

Find out more

Pec

Evolution p.308
Mammals p.334
Skeletons p.352

>PLE AND PIANET P .

Fact finder p.422

374

336

nucleus.

HOW LIVING THINGS WORK

Each kind of living thing is adapted to
the world around it. A gibbon’s long
arms enable it to swing through the
treetops. Forward-pointing eyes
make it good at judging
distances as it swings
from one branch to
the next.

ORGANISMS AND
THEIR ENVIRONMENT
All living things, or organisms,
need to fit in with their
environment. They take in
food from the world around
them. They put the food to
many uses, including
producing energy for
moving, and raw materials for growing
and reproducing. Through evolution,
living things have developed different
ways of getting their food. A gibbon is
good at reaching leaves and fruit high
in the treetops. Its body can break
down this food to release the nutrients
and energy that it contains.

Why ARE PLANTS GREEN? What is blood for?
Is your skin dead or alive? In many cases, the
answers to these questions lie in the make-up
of living matter: living things contain
different parts, which fit together amazingly
well to make them work. In plants and
animals, some of these parts are big enough
to see, but others are so small that they can
only be looked at through a microscope.
In all living things, even the smallest
parts can be very complicated. By
finding out exactly how the
small parts work, scientists
have been able to see how
whole organisms work.

ORGANS

The gibbon’s body contains a
set of organs. They include its
brain, heart, lungs, and liver. An
organ is a structure that carries out
particular tasks in the work of staying
alive. Each one has a characteristic
shape, and is made up of several
different kinds of cells.

The body machine

An animal’s body is like a gigantic city of separate
parts. The smallest of these parts are called cells.
There are many types of cells in living things.
Together they provide all the services that the body
needs, from energy supply and communication to
waste disposal. A single animal or plant may contain
billions of cells arranged in a very precise way.
Everything each cell does is controlled by its nucleus

ANDREAS VES ALIUS

Vesalius (1514-64) founded
the modern science of
anatomy, which looks at the
structure of living things. He
was Belgian, but he did his
most important work in
Italy. He became a professor
of anatomy at the age of 23,
and in 1543 he published a
book called The Structure of
the Human Body . It was based on careful observation,
and was beautifully illustrated. This was the first book
to show details of the body in an accurate way.

CELLS

Cells are the smallest parts of
a living thing that are fully
alive. The cells in an organ are
arranged in groups called
tissues. Each tissue contains cells
of one type, and it carries out a
limited range of tasks.

GENETIC CODE
Almost every cell has a control
centre called the nucleus. Packed
inside it are long molecules of a
substance called deoxyribonucleic
acid, usually referred to as DNA.
Each DNA molecule is a double
helix (spiral), and its two strands
are linked by chemical “bridges”.
The exact sequence of these bridges
makes up the cell’s genetic code,
which is like a recipe for what the

cell does and how it works.

The liver is one of the gibbon’s biggest
organs. It processes digested food,
carries out many chemical
reactions, and stores
substances that are used to
produce energy.

Hepatocytes are one kind
of cell in the liver. They are
arranged in sheets, and
they make a fluid called bile,
which helps in digestion.

Hepatocytes form one
kind of tissue in the
liver. There are
other kinds of cells
in the liver, which
form other kinds
L of tissues, such
as blood
i - vessels.

Strands of

DNA are

found in the

337

HOW LIVING THINGS W ORK

Cells

Every LIVING THING is made up of cells. Each one is
like a microscopic factory, where thousands of chemical
reactions happen in a carefully controlled way. Cells use
these reactions to perform all the tasks involved in being
alive. Cells can divide in two over and over again. Some
living things, such as amoebas, are just one cell. Others,
such as ourselves, have millions of cells that all work
together. Within an organism, the cells in
different tissues are slightly different.

Special proteins in
the membrane carry
complex substances
in and out of the cell.

PLASMA MEMBRANE
The plasma membrane encloses
the whole cell, but it has pores in
it. These pores let some chemicals
through, but not others. This
means the membrane is

semipermeable, which is very
important, because then it
can “choose” the
chemicals it lets in
and out of a cell.

Plant cells are different to animal cells in
in two ways. They have stiff cell walls
and can make their own food.

plasma
membrane is
made of a double
layer of molecules.

Typical animal cell

Vacuoles are
storage areas
in the cell.
They are used
to store fats, for
example.

The DNA in the
nucleus stays
inside it, but
the instructions in
it are copied and
carried to different
parts of the cell.

Animal cells

An animal cell is like a tiny,
fluid-filled, squashy bag. The
cell is held together by a thin,
flexible layer called a plasma
membrane. The membrane is
semipermeable, meaning that
it allows some chemicals to
pass through it, but not
others. At the heart of the
cell is the nucleus, which
controls everything that
happens inside the cell.
Around the nucleus is a jelly-
like fluid called cytoplasm.
The cytoplasm contains tiny
structures, called organelles.
Each kind of organelle
carries out a different
set of tasks.

in the membrane around
the nucleus (called the nuclear
membrane) allow copies of
the DNA code to travel
out of the nucleus.

NUCLEUS

The nucleus is the cell’s
command centre. It
contains chemical
instructions in molecules
of DNA (deoxyribonucleic
acid) for everything that the cell
does. Normally, the DNA is spread out in long
strands. The nucleolus is a round “blob” inside the
nucleus. It makes organelles called ribosomes.

Smooth endoplasmic
reticulum makes lipids
(fat molecules).

Plasma membrane

Ribosomes are small
organelles that make
proteins. Ribosomes
either float in the
cytoplasm, or are
attached to the
endoplasmic reticulum.

Rough endoplasmic reticulum

Cytoplasm is a jelly-like
fluid containing
organelles. It often flows
around inside the cell.

A mitochondrion is an organelle that
produces energy for the cell. It breaks
down substances to release energy. The
folds inside a mitochondrion give a large surface
area for these reactions to take place.

Ribosomes on
the surface of
rough

endoplasmic
reticulum (RER)

ENDOPLASMIC
RETICULUM
The endoplasmic
reticulum (ER) is
the work surface of
the cell. It is a system
of double membranes on
which chemical reactions take
place. The membranes are
folded up, and packed together
like the layers in a sandwich.
They link up with the
membrane around the nucleus,
and with the plasma membrane
that encloses the cell.

Rod cells from a human eye measure
40 micrometres long, compared to
ostrich eggs, which measure
250,000 micrometres across.

An ostrich
egg weighs
up to 1.5 k n
(3 lb 5 oz).

HOW BIG IS A CELL?

Most animal cells are between 10 and 20 micrometres
( 1 /100th to V50th of a millimetre) across,
while plant cells are slightly larger. But
cells vary enormously in size. The
smallest free-living cells are bacteria
called mycoplasmas. Their cells are
about 0.1 micrometres ( J / 10,000th
of a millimetre) across. Eggs are giant cells. An
ostrich egg cell can be up to 25 cm (10 in) long,
which makes it the largest cell that we know of.

This false-
colour electron
micrograph of
rod cells from
the eye shows
four cells. The
two round cells
are nerve cells.

CELLS

1590 The Dutch optician
Zachariasjanssen invents the
compound microscope (a
microscope with more than
one lenis). This makes tiny
objects visible for the first time.

1665 The English scientist
Robert Hooke (1635-1703)
looks at thin slices of plants
through his microscope. He
sees box-like shapes, and calls
them “celfsA

1838 Two German doctors,
Theodor Schwann (l§J0-82)
and Jakofe Mathias Schleiden
(1804-81), suggest that all
living things are made of cells.

1937 Edouard Chatton, a
French biologist, notices that
some microorganisms
(prokaryotes) have cells that
are quite different to those of
all other living things.

Nerve cell

i ^s w h hhhh!

338

HOW LIVING THINGS WORK

Plant guard
cells

Pi ANT CELLS

A plant cell is different from an animal cell in two important ways. As well
as being surrounded by a plasma membrane, it also has a stiff cell wall. A
plant cell also contains organelles called chloroplasts, which give it a
green colour. Chloroplasts catch the energy in
sunlight for the cell to make its own food.

Most plant cells also contain large
vacuoles, which store cell sap. The
sap presses against the walls of
the cell, keeping it in shape. A
plant wilts when it lacks water
and the sap does not press
against the cell wall.

The plasma membrane lies _||.

between the wall and the
cytoplasm inside the cell.

Chloroplasts are scattered _
throughout the cytoplasm. They get
their green colour from a pigment
called chlorophyll. Cells in roots and the
inside of stems do not have chloroplasts.

Vacuole filled with cell sap

Mitochondrion

Animal

(mammalian) red
blood cell

DIFFERENT SHAPES
FOR DIFFERENT WORK

The different cells in plants and animals
are specialized, meaning that they can
carry out only one kind of work. A fat cell is
filled with fat either permanently or until it
is needed for energy. A nerve cell carries
messages from one part of the body to
another, and a muscle cell contracts to
make part of the body move. Red blood
cells carry oxygen in animals, and sieve
cells carry nutrients in plants. Unlike most
cells, these two kinds do not have nuclei.
Guard cells are found in plant leaves,
controlling the pores that allow air into the
leaf. They also have chloroplasts to harness
the energy in sunlight.

LOOKING AT CELLS
Most cells are f ar too small to see with eyes
alone. To look at them, biologists have to
use microscopes. A light microscope can
magnify clearly up to about 2,000 times.
Special stains or lighting are used to
make different parts of the cell stand
out. An electron microscope works in
a different way. It can magnify over a
million times, but normally it cannot
be used with living specimens. A
scanning electron microscope gives an
almost three-dimensional image.

Light micrograph of
hepatocytes (liver cells)
magnified 56 times. The
cells have been stained to
make them easier to see.
The nuclei absorb the dye,
giving them a dark colour.

Electron micrograph
of liver cells,
magnified 90 times
and artificially
coloured. Electron
microscopes can
produce small
magnifications as
well as large ones.

BUILDING A WALL
Plant cell walls are made of
a tough material called
cellulose. The cell makes
tiny cellulose fibres, and
builds them up in criss-cross
layers on the outside of its
plasma membrane. The
cellulose layers make a
strong, stiff box. Without
their tough cell walls, most
plants would collapse into a
green sludge.

Light micrograph of
Lactobacillus
bulgaricus, a
bacterium found in
live yoghurt. It is
illuminated with
green light and
magnified 400 times.

Scanning electron micrograph
of Lactobacillus bulgaricus
magnified 1,000 times.
Electron microscopes
produce a black and white
image. Here, the image has
been artificially coloured by
a computer.

Typical bacterium

Molecule of
DNA loose in
cytoplasm _ _

Plasma

membrane _

Cytoplasm _

Thick cell walL - '

outside plasma
membrane

Whip-like flagella that
move the bacterium

Light micrograph of
muscle fibres,
magnified 140 times.
Several nuclei can
be seen, as well as
the striations
(stripes) that are
typical of muscles
that pull on bones.

SIMPLEST GELLS
The cells of bacteria
and other micro¬
organisms do not have
nuclei or mitochondria. They are
called prokaryotic. Other cells, such
as plant and animal cells, do have
nuclei, and are called eukaryotic
cells. They are more common.

Artificially coloured
electron micrograph of a
single muscle fibre,
magnified 1,940 times.
The fibre is made up of
many parallel fibrils.

Each fibril is just 1/500th
of a millimetre across.

Find out more

HOW SCIENTISTS WORK 1\1 4
Vision p.204

Single-celled organisms p.314
Bacteria p.313
Photosynthesis p.340
Cellular respiration p.346

339

HOW LIVING THINGS WORK

Photosynthesis

WHY ARE MOST LEAVES GREEN?

IMAGINE BEING ABLE TO MAKE FOOD just by standing in sunlight.
This is what plants do when they carry out photosynthesis. The word
photosynthesis means “putting together by light”. During this process,
plants collect energy from sunlight. They use this energy to turn water and
carbon dioxide into a simple sugar called glucose. Plants then use glucose
to fuel their cells, and also to make other substances, such as starch and
cellulose. Plants are not the only living things that carry out
photosynthesis. Some protists and monerans also make food in this way.

Photosynthesis takes carbon dioxide and water and
produces glucose and oxygen. The equation is:

6CO2 + 6H2O —> CgH^Og + 6O2

Sunlight is made of many colours.
Most plants contain a green
pigment called chlorophyll, which
reflects the green part of light. It
captures the blue and red parts of
sunlight, and uses them to drive
photosynthesis. Plants such as the
copper beech in the woodland
above, and red and brown
seaweeds, also use other pigments
as well as chlorophyll to capture
different colours in light. That is
why they are not green.

Oxygen

molecule

Water

molecule

Carbon

dioxide

molecule

Glucose '
molecule

The plant uses glucose for
energy, and for making
other substances, such as
simple sugars and starch. It
releases oxygen into the air.

A plant collects
carbon dioxide from
the air, and water
from the soil. /

HOW PHOTOSYNTHESIS WORKS

Most plants carry out photosynthesis in
their leaves. Many of the cells in a leaf
contain tiny organelles called
chloroplasts. Chlorophyll and other
pigments in the chloroplasts trap the ,
energy in sunlight. Once the energy
has been trapped, it powers a
plicated series of chemical

When light
shines on a piece
of pondweed,
bubbles of
oxygen float up
into the test-tube.

The energy
C in sunlight is
trapped by
chlorophyll and
other pigments as the
light passes through a

Pondweed
covered by
glass funnel

com

reactions. During these reactions,
water molecules are split apart into
hydrogen and oxygen atoms. The
hydrogen atoms combine with carbon
dioxide molecules to make glucose, and
oxygen is given off as a waste product.

The underside
of the leaf has
', I tiny pores,

*• V called stomata,
f* j This is where
{ carbon dioxide
V and oxygen enter
and leave the leaf.

Chloroplast

INGENHOUSZ

At one time, people
gjWEjjPthought that plants
grew simply by
absorbing substances
from the soil. But
IMF ' F . 1 . . in the 18th

y. f century, it was

XrJ found that

ijp’Mjjfc they needed

V v air as well. The
Dutchman Jan
Ingenhousz (1730-99) discovered
that plants take in carbon dioxide
and release oxygen when sunlight
shone on them. He found that the
gases travel in the opposite
direction when it is dark.

Stoma

MAKING OXYGEN
Normally, we cannot see the
oxygen that is released by plants.
But when water plants carry out
photosynthesis, oxygen sometimes
forms bubbles on the surface of
their leaves. Water plants get
carbon dioxide dissolved in the
water around them.

GHLOROPLASTS
Most cells inside a leaf contain
dozens of chloroplasts. Each ^
one is made of piles of tiny
discs. The surface of each iHH

disc contains chlorophyll JESS
and other pigments, which
trap the energy in sunlight.

Chlorophyll spread over
the surface of discs

Find out more

AUTUMN LEAVES
^ In autumn, many trees break
||J down the chlorophyll in their
leaves. The leaves are then
yrf coloured by any pigments left
behind. These include
carotenoids, which make carrots
orange, and anthocyanins, which
make some apples red.

Describing reactions p.53
Light p.190
Colour p.202
Digestion p.345
Celluiar respiration p.346
Growth and
DEVELOPMENT P.362

340

HOW LIVING THINGS WORK

Transport in plants

If YOU FORGET TO WATER an indoor plant, it will

eventually wilt and die. This happens because plants need
| \ water to survive. Water travels upwards through a

plant’s roots and stems, and it evaporates into the air
' A from its leaves and flowers. This movement is
' called transpiration. It keeps the plant’s cells firm,

and it also carries dissolved minerals up from the
^, T so ji plants also have another transport system,

called translocation, which often works in the
Bjow* other direction. It carries food substances away
1 ’M t from the leaves into the buds, shoots, and roots.

When the water
reaches a leaf, it
evaporates through the
pores on the underside.
They are called stomata.

Food substances
made during
photosynthesis move
away from the leaves
and down the plant
through phloem cells.

Phloem

TWO-WAY TRANSPORT
Water travels up a plant through
xylem cells. These are cylindrical
cells that link end to end. They
eventually die, leaving tiny fluid-
filled pipelines that stretch from the
roots and up into every leaf.
Dissolved food substances travel
through a different system of
pipelines made by phloem cells.

Phloem

carries

food

Xylem

carries

water

Vascular bundle FEEDING ON SAP

The sugary fluid in phloem cells makes
an energy-rich food for sap-sucking
insects. Aphids pierce the stem and
ragg&flNKgK phloem cells with their sharp
Ibly \ mouthparts, and then drink the fluid

which oozes out. Sometimes there is too
J much sugar for an aphid to digest. The
■K leftover sugar passes out of its body in

drops of sticky liquid called honeydew.

Transpiration

Every day, a large tree loses about
1,000 litres (220 gallons) of water from
its leaves. But what makes the water
upwards? It is both pushed and

move

pulled. The roots often push the water
upwards a little way. The water that
evaporates from the leaves draws up more
water to take its place. This happens partly
because water molecules attract each other,
and partly through osmosis^

Lady's mantle

(Alchemilla vulgaris )

Water
moving up
plant from
the roots

TUBES FOR TRANSPORT
Xylem and phloem cells are clustered
together in groups called vascular
bundles. The xylem is on the inside,
and the phloem on the outside.
Xylem cells are often strengthened,
which keeps the tubes open so that
liquids can pass up them easily.

Slice of celery stem,
showing xylem cells
stained by dye

OSMOSIS

If you put a peeled potato in
very salty water, water will be
sucked out from its cells. If
you put it in tap water, the
cells will absorb water. This
flow of water into and out of
cells is called osmosis. During
osmosis, water always flows

GUTTATION

In low-growing plants, water is
sometimes pumped upwards by the
roots faster than it is lost by the
leaves. When this happens, water
droplets form around the leaf edges
because the water does not evaporate
fast enough. This is guttation. It
usually occurs after dark, and only
when the air is still and humid.

A cube of potato
was left in very
salty water for a
day, and shrunk
slightly because
water was
sucked out of it
by osmosis.

Evaporation from
leaves draws water
and dye up through
celery stem.

SEEING TRANSPIRATION
You can see transpiration at work
by putting a stick of celery into
some water containing a food dye.
As water evaporates from the
leaves, water travels up the celery
and carries the dye with it. The dye
shows that the water moves
upwards through narrow channels,
which are the xylem cells.

through a semipermeable
membrane. It always flows
from the side that contains a
bigger proportion of water
molecules to the side that
contains a lower proportion
of water molecules and more
dissolved substances.

A cube of
potato of the
same size was
left in tap water
for a day, and it
swelled slightly
because water
was absorbed
by osmosis.

Find out more

Kinetic theory p.50
Colour p.202
Flowering plants p.31 8
Cells p.338
Photosynthesis p.340
Asexual reproduction p.366

341

HOW LIVING THINGS WORK

Nutrition

EVERY LIVING THING needs nutrients (raw materials) to stay alive.

Nutrition is the process by which they get these substances, and put them to
work. Like all animals, we get our nutrients by eating food. This is
called being heterotrophic. Food contains three main kinds of
nutrients: proteins, fats, and carbohydrates. We use proteins
to build and repair our bodies, and fats and carbohydrates
mainly for fuel. We need other nutrients, but in smaller
amounts. These substances are minerals, used to build
important molecules in the body, or vitamins, which enable
particular chemical reactions to take place. Plants live in quite
different way. They make their own food, which is called
being autotrophic. They only need simple nutrients, such as
carbon dioxide, water, and mineral salts from the soil.

Hummingbirds
get the energy
to hover in front
of flowers from
nectar, which is
rich in sugars.
But nectar
contains very
little protein, so
hummingbirds
also eat a few
insects.

KEEPING A BALANCE
Good nutrition means eating the
right food in the right proportions.
Here is a meal that has a range of
different foods, which gives a
balance of proteins, fats, and
carbohydrates, as well as a range of
minerals and vitamins. That’s why it
is important to eat a wide variety of
food, rather than too much “junk”
food, such as crisps, which mainly
provide fats and carbohydrates.

DIET?

To a scientist, a diet has nothing
to do with slimming. Instead, it means an
animal’s complete food intake. Some animals
have a very varied diet. Others are much more
choosy. An adult hummingbird lives mainly on nectar, a sugary
liquid made by flowers. Nectar is packed with carbohydrates,
which means that it is a good source of energy.

This swallowtail
butterfly caterpillar
(Papilio machaon)
eats almost all the
time it is awake.

CARNIVORES

A pike is a carnivore - an animal that feeds on other
animals. Its food is rich in nutrients, so a single meal
can last for a long time. However, its food is not always
easy to obtain. Carnivores such as the pike often
have to put a lot of energy and time into finding
and catching a meal.

OMNIVORES
Raccoons, bears, and
humans are omnivores,
meaning that they can feed
on both plant and animal
food. Omnivorous animals
are not very choosy, so they
can usually Find something
to eat. Raccoons are
particularly good at living
on people’s leftovers.

MALNUTRITION

If an animal’s diet is missing a
particular kind of nutrient, it
becomes malnourished. Its
health declines, and it may
suffer from a “deficiency
disease”. In some parts of the
world, children suffer from
kwashiorkor, which is a
deficiency disease caused by a
lack of protein. Plants, too,
become unhealthy if important
minerals are missing in the soil.
These cherry leaves are suffering
from magnesium deficiency.

HERBIVORES

Many kinds of animal, from caterpillars to elephants, live entirely on
plant food. They are called herbivores. Their food is of ten not very
nutritious, and to get enough energy and nutrients to live,
they have to spend a large part of their lives
eating. Some herbivores, like camels, have
bacteria in their digestive systems to help
them release the nutrients from their food.

Find out more

Chemistry of food p.78
Arthropods p.322
Fish p.326
Feeding p.343
Teeth and jaws p.344
Digestion p.345
Food chains and webs p.377
Fact finder p.422

342

HOW LIVING THINGS WORK

Feeding

SAFETY IN A HERD

LONG AGO, PEOPLE GOT THEIR FOOD by gathering seeds and fruit,
and by hunting animals. Nowadays, most of our food is produced by
farming. Instead of gathering food ourselves, people who live in towns
and cities buy it in shops. But in the natural world, things are very
different. Wild animals spend a large part of their time either feeding, or
trying to find their next meal. The way that they do this depends on what
they eat. Herbivores (animals that eat plants) do not usually have to look
far for their food, because plants are rooted in one spot and cannot run
away. Carnivores (animals that eat meat) usually have to track down their
prey, and overpower it. However, some animals, such as barnacles or sea
anemones, stay in one place and wait for their food to come within reach.

Gazelles feed on grass, in the open
country of the African plains. They
have many enemies, and their only
defence is to run away. Gazelles make
themselves safer by living in herds.
While some of the gazelles are eating,
others keep a watchful eye for any
signs of danger.

This jackal distracts
the mother gazelle
away from the baby.

■

WORKING IN A TEAM
Some hunting mammals catch their

prey by working together. Here, one jackal attacks the mother gazelle,
even though an adult gazelle is too big for it to kill. While the mother is
distracted, the other jackal pounces on her youngster. By
working as a team, the jackals get a meal that

one jackal could not catch on its own.

Predator and prey

The common shrew (Sorex artmeus) is one of the smallest of all
predatory mammals (mammals that hunt). It measures just
7.5 cm (3 in) from head to tail, and is about as heavy as a sugar
cube. Despite its tiny size, it is a fierce hunter with a large
appetite. It overpowers earthworms with its sharp teeth, and
quickly starts to feed. A shrew needs to eat its own body mass in
food every day, or it will die. Larger predatory mammals eat
much less, because their bodies use
energy at a much slower rate.

FEEDING ON
LEFTOVERS

Several different
fungi are living on
food substances in
this piece of bread.
Instead of eating whole
pieces of bread, they
absorb food chemicals
through a mass of tiny threads.
Fungi and bacteria are important
because they help to break down
the dead remains of living
organisms. Those that do this are
called saprophytes, or saprobes.
Other fungi live on things that are

still alive.

FILTER FEEDING

This fanworm (.Protula intestinum ) lives by filtering
tiny particles of food from water. Its “fans” are
rings of tentacles. The tentacles trap particles of
food, and tiny hairs then push the food towards
the worm's mouth. Many different animals live
by filtering food They include molluscs, such as
oysters and mussels, and sponges and sea
squirts. Small filter-feeding animals usually
spend their adult lives in one place. The biggest
filter-feeders of all, whales, filter food as they swim
along.

UNDERWATER NET
The larvae of
caddisflies live in
streams. Most of
them find their food
by crawling about,
but some have a
different technique.
They make nets from
silk, and then sit
inside the neck of the
net. Small animals
are swept into the net
and then eaten.

Find out more

Chemistry of food p.78
Fungi p.315

Jellyfish, anemones, and
corals P.320
Molluscs p.324
Mammals p.334
Teeth and jaws p.344
Growth and development
p.362

Food chains and webs p.377
Factfinder p.422

343

HOW LIVING THINGS WORK

TEETH FOR GNAWING
A coypu’s chisel-shaped incisor
teeth grow throughout its life.
Each incisor has enamel only on
the front face. The back of the
tooth wears away fastest, leaving a
front edge that is always sharp.

Teeth and jaws

What IS THE HARDEST PART of your body? It
is the surface of your teeth. This surface is made
of enamel, which protects teeth from wearing
away, and helps to stop them being attacked by
chemicals in food. Teeth cut and grind your food
so that it can be digested. Most mammals have
specialized teeth that are shaped to carry out
different tasks: some teeth cut and slice, others
grip or crush. Our teeth grow in two separate sets,
and once a tooth has appeared, it does not grow
any bigger. Animals that feed by gnawing have

chisel-shaped teeth that never stop growing.

CUTTING THROUGH FOOD
A dog’sjaw muscles are strong
enough to crack bones. When a
dog feeds, its jaw moves up and
down like a pair of scissors. Plant¬
eating animals have jaws that
move f rom side to side as well as
up and down.

Self-sharpening
incisor teeth

Incisors

Diastema

HERBIVORE
TEETH

The coypu is a typical herbivore - an animal
that only eats plants. Its long incisor teeth cut
through tough plant stems, while its molar
teeth grind up its food. A gap called the
diastema separates the two groups of teeth.

Human teeth

Humans are omnivores, meaning that we
eat both plant and animal food. We use
our front teeth (incisors) for biting into
our food, and our cheek teeth (molars) for
chewing it. We also have small canine teeth,
which we use for gripping. The jaw is pulled
upwards by powerful muscles that connect it
to the cheek bones and temples. When you
chew, you can feel these muscles tightening.

Teeth fit into
special sockets
in the jaw.

SIMPLE TEETH
Not all animals have specialized teeth
like those of mammals. Reptiles,
such as this crocodile, have
identical teeth that are
shaped like pegs. A crocodile
cannot chew its food. Instead, it wedges
the food under something solid, tears it
apart, and swallows it in chunks.

ANIMALS WITHOUT TEETH
Many animals have hard
mouthparts instead of teeth. This
dragonfly larva grabs its prey with
a special hinged “mask”. The
mask shoots out to catch passing
animals. Many plant-eating insects
(such as grasshoppers) have a
stomach chamber that grinds up
their food after they have swallowed it,

Enamel on

crown

Pulp cavity

Root

Blood

Carnassial

teeth

Canine

teeth

Flap of
bone for
anchoring jaw

CARNIVORE TEETH muscles

A dog is a typical carnivore - an animal that
eats mostly meat. At the front of its jaw, it has
long canine teeth that grip its food. Towards
the back, it has sharp carnassial teeth that
slice up food so that it can be swallowed.

Permanent teeth

Incisor

Canine

A nerve runs
alongside the
blood vessels.

INSIDE A TOOTH
The part of a tooth that you can see is
the crown, which is only about half of it.
The crown is covered with enamel, and
underneath is a layer of hard dentine.
The core of the tooth is filled with soft
living pulp, which is supplied with
blood. Long roots and a special cement
keep the tooth anchored in the jaw.

Premolar

Molar

Third molar
(wisdom
tooth)

HUMAN
DENTITION
Your first set of
teeth (your milk
teeth) contains eight incisors,
four canines, and eight molars.

Most people have 32 teeth in
their second set, known as the
permanent teeth. The wisdom
teeth are the last to appear,
although not everybody has them.

Cement holds the
root in the jaw.

Jawbone

Find out more

Arthropods p.322
Reptiles p.330
Mammals p.334
Feeding p.343
Digestion p.345
Skeletons p.352

344

HOW LIVING THINGS WORK

Digestion

SECOND-HAND FOOD
Termites cannot digest the cellulose
in plants themselves, so some get a
fungus to do it for them. They pile
up pieces of leaves underground, and
use this to grow a fungus. The fungus
digests and takes in the plant food.
The termites then eat pieces of the
fungus, which they can easily digest.

During DIGESTION, all the complicated
substances that food is made of (carbohydrates,
proteins, and fats) are broken up into much
simpler compounds that your body can absorb.

Digestion starts almost as soon as you put food
into your mouth. As the food travels through
your stomach and into your small intestine,
different enzymes (special proteins) digest
carbohydrates, fats, and proteins. The products
of digestion are absorbed through the intestine
wall, and anything you do not digest passes
straight through your body. Digestion is the first
step in getting energy from food.

Oesophagus
(gullet)

Small

intestine

Stomach

Caecum

Appendix

Normally a
mouse's digestive
system is packed
into its abdomen.

Here it has been
spread out to make
it easier to see.

Gall
bladder

Pancreas

Liver

Grains
of wheat

are full of

starch

EXTERNAL DIGESTION
Spiders have tiny mouths, and they
digest their food before they
swallow it. When a spider catches
an insect, it injects it with a liquid
that contains enzymes. The
enzymes break down the sof t parts
of the insect’s body, and the’spider
sucks up the nutritious liquid.

Digestion in a mouse

When a mouse swallows, its food
travels first to its stomach. Here,
it is partly broken down by a
strong acid. It passes on through
the small and large intestines,
which absorb all the products of
digestion and water. The mouse’s
pancreas produces substances that
neutralize the stomach acid. Its
caecum is a dead-end chamber
where plant food is digested.

Glucose is Of
made by J
splitting
starch
molecules.

Digestive
enzymes break
the links between
the sugar units.

HOW A COW DIGESTS GRASS

Cows digest grass with the help of
microorganisms and a four-part
stomach. First the food goes into

DIGESTING STARCH
Wheat, rice, and potatoes all # *

contain starch, a substance that plants
make as a food store. Starch molecules
contain hundreds of sugar units, linked to form
long chains. During digestion, these chains are broken up by
enzymes. The result is many molecules of glucose, a simple
sugar that can be absorbed by the body.

Each starch molecule
produces many
molecules of glucose.

Starch
molecules are
too long to be
absorbed so
they must be
digested.

the rumen and reticulum so that
microorganisms can break down
cellulose. The cow then brings up
the food to chew it again. The food
goes on to the other stomachs to be
digested. We cannot digest the
cellulose in plants, and it passes out
of our bodies as roughage or fibre.

DIGESTING PROTEINS AND FATS
If you eat a piece of meat, the proteins and fats it contains are
broken down into much smaller molecules, to be absorbed in
your small intestine. Proteins are digested to produce chains
called polypeptides, and these in turn are broken down to
make amino acids. Fats are turned into tiny droplets, and are
then broken down to form glycerol and fatty acids.

A protein molecule is made
up of many amino acids.

It takes several
enzymes in the
stomach and in the
small intestine to
digest proteins.

Amino acid molecules

■f*

A fat molecule is made of
glycerol and fatty acids.

Glycerol

molecule

Fatty acid
molecules

Fats are turned into
droplets by bile, a
fluid from the gall
bladder. The droplets
are digested by
enzymes in the small
intestine.

Find out more

CHE^

Cell

Catalysts p.56

IISTRY OF THE BOD

EMISTRY OF FOOD F

UIAR RESPIRATION

Yp.76

•.78

p.346

345

IIOW LIVING THINGS WORK

Cellular respiration

■m

Respiration works like a
turnstile: it releases energy
as and when it is needed.

MANAGEABLE ENERGY
Aerobic respiration is very like burning,
because it combines food substances (the fuel)
with oxygen to release energy. But there is an
important difference. Burning happens very
quickly, and it releases energy in a sudden rush.
Aerobic respiration involves many chemical
reactions, and it releases energy in a much
more controlled and manageable way.

Chinese hibiscus
(Hibiscus rosa-
sinensis)

All living things need energy to survive. Your energy

comes from food. After you digest a meal, food substances travel in
your blood and then into your cells. Here, they are respired, which
means that they are broken down so that their energy can be
released and put to work. In anaerobic respiration, food substances
(mainly glucose) are split apart without using oxygen, and a small
amount of energy is released. In aerobic respiration, food
substances are combined with oxygen, and carbon dioxide and
water are produced as waste products. This kind of respiration
; takes place inside a cell’s mitochondria, and releases a lot
^ more energy. Aerobic respiration supplies most of the

energy that your body needs.

0=0

One

glucose

molecule

During respiration, one
molecule of glucose is
combined with six
molecules of
oxygen.

Six oxygen
molecules

0=0

Respiration takes glucose and oxygen and produces
energy, carbon dioxide, and water. The equation is:
c 6 h 12°6 + 60 2 —> energy + 6C0 2 + 6H 2 0.

RESPIRATION
IN PI ANTS

During daylight hours, a plant
builds up food (glucose and starch)
by photosynthesis. It also breaks down
some food by respiration. It makes more
food than it breaks down, so its leaves take
in carbon dioxide. At night, photosynthesis
stops. Then the plant only breaks down food
by respiration, so its leaves take in oxygen.

A mitochondrion ^
contains folded
membranes that
create large work
surfaces on which
reactions can
take place.

Six molecules of
carbon dioxide _

///

HANS KREBS

The German
biochemist Hans
Krebs (1900-81)
discovered exactly
what happens
when glucose is
respired by cells.
Krebs knew that a
glucose molecule was
split to make pyruvic
acid, a simpler substance.
However, no-one knew what
happened to the pyruvic acid.
Krebs dicovered that it joins an
endless cycle of chemical
reactions, now known as the citric
acid cycle or Krebs cycle. Energy is
released at each turn of the cycle.

Energy
released
during

respiration has
to be stored. The
energy is used to
turn ADP (adenosine
diphosphate) into ATP
(adenosine triphosphate).
When energy is needed,
ATP is broken down into
ADP to release it.

A*'-.

Six molecules of water

What happens during respiration

The human body is powered mainly by glucose. This
is a sugar that you get by digesting starch and other
carbohydrates in your food. Before glucose can be respired,
it has to be broken down into a simpler substance, pyruvic
acid. This travels into the cell’s mitochondria, where it is
combined with oxygen to produce carbon dioxide and
water. During this process, lots of energy is released. The
energy can be used to make muscles work, for example.
Aerobic respiration is exactly the opposite of
photosynthesis, which uses energy to make glucose.

ANAEROBIC RESPIRATION

If you sprint very quickly, your muscles run out of oxygen.
Without oxygen, your muscles cannot turn glucose into water
and carbon dioxide. Instead, they turn glucose into a
substance called lactic acid (too much of this gives you
cramp). This is anaerobic respiration, because it does not use
oxygen. Later, when you have stopped running, the lactic
acid is broken down using oxygen. Some organisms, such as
yeasts and bacteria, can live entirely by anaerobic respiration.

Find out more

Phosphorus p.43
Oxygen p.44
Fermentation p.80
Cells p.338
Photosynthesis p.340
Digestion p.345
Fact finder p.422

346

HOW LIVING THINGS W ORK

Breathing

Every time you take a breath, you suck air into

your lungs. The oxygen in the air diffuses (spreads)
through the thin lining of the lungs, until it reaches the
blood in the tiny blood vessels in your lungs. It is then
loaded on to red blood cells, and carried to all parts of
your body. At the same time, the waste gas carbon
dioxide (from cellular respiration) moves in the other
direction, so that your body can get rid of it. Mammals,
birds, amphibians, and reptiles all have lungs. Fish
breathe through thin flaps called gills, and insects have
tiny air pipes running through their bodies.

The larynx is a
passageway made of
cartilage. It contains
vocal cords. When
these are vibrated by
air, they make sounds.

You have two
lungs, but they are
not the same
shape. Your right
lung is broader,
and has three
lobes. The left lung
has just two lobes.

The trachea, or windpipe,
leads from the larynx to the
lungs. It is held open with
C-shaped rings of cartilage.

Your lungs are surrounded by your
ribs, and they sit on a dome of
muscle called the diaphragm. When
you breathe, your ribs and
diaphragm change the shape of
* your lungs. Air is either sucked
into the lungs, or squeezed out. The
amount of air that moves depends
on what you are doing. When you sit
still, only a little air moves with each
breath. When you exercise, you
breathe faster and more deeply.
Each deep breath moves up to six
times more air as when you sit still.

Air moves
out of lungs

Ribs move
downwards

Your lungs \
are close
together.
They are
illustrated
apart here
to show the
airways
clearly.

Diaphragm moves upwards

When you breathe out, your
ribs move downwards and
your diaphragm springs
upwards. This reduces the
space around the lungs, so
that air is squeezed up
through the trachea
(windpipe).

Hiccups happen when
your diaphragm
contracts suddenly.

Spiracles allow air into the
tracheal system. They can be
opened and closed.

INSIDE A LUNG ,

Your lungs are like a pair of large sponges.
They have a very rich supply of tiny blood
vessels called capillaries, and they are Filled
with a network of branching air passages. The
smallest passages end in dead-end spaces,
each called an alveolus, where the air and
blood are brought close together. All the
alveoli put together have a huge surface area -
about 40 times that of your skin. This enables
large amounts of oxygen and carbon dioxide
to pass into or out of your body.

Alveolus

Bush cricket
(Ephippiger
species)

Tracheae
lead from the
abdomen to
the thorax
and head .

TRACHEAL
SYSTEM
Insects breathe
through a network of air-
Filled tubes, called tracheae. These
lead deep into the insect’s body, and
divide into branches that are fine
enough to reach right into its
muscles. The tracheae are
sometimes connected to air sacs,
which can change shape just like our
lungs. Each trachea opens to the
outside through a small hole called a
spiracle in the insect’s body case.

In an alveolus, blood and air are
so close together that oxygen
and carbon dioxide can easily
move between them.

E ac h \

^ filament
carries tiny flaps,
and oxygen goes into
the flaps to reach the
fish's blood.

Tracheae carry oxygen
directly to an insect’s cells.

fggg BREATHING WITH GII.I.S

Water contains oxygen, although much less than air

PS■ *“ does. Fish collect oxygen using their gills. A gill is a
r series of tiny flaps that have a rich blood supply, like
our lungs. The fish takes in water through its mouth.

JF As the water washes over the gills, the gills collect
oxygen, and give up carbon dioxide. The water then
flows out through one or more slits on the fish’s body.

Find out more

Making and hearing
sound p. 182

Celluiar RESPIRATION P.346
Blood p.348
ClRCUIATION P.349
Internal environment p.350

A fish's gills are
just behind its head.

Gills are made up of curved
arches, which have feathery
projections called filaments.

347

HOW LIVING THINGS WORK

Blood

Blood IS AN AMAZING SUBSTANCE. It is like a fluid
conveyor belt that carries oxygen to every living cell in your
body. It also transports food substances, hormones, waste
products, and warmth, and it acts as your body’s main
defence against disease. If you look at a drop of blood, it
seems to be just a red liquid. But under a microscope, the
same drop turns out to be packed with millions of cells,
floating in a watery fluid. The red blood cells carry oxygen,
and the white cells attack anything that invades the body
from outside. The plasma (the liquid part) carries most of
the carbon dioxide. You have about 4 litres ( 6^2 pints) of
blood. Its cells are squashed, squeezed, and battered. Every
day, millions of them are replaced.

Blood

plasma

Platelet

White blood cells can
change shape. They
squeeze through the walls
of the smallest blood
vessels to fight infections.

Red

blood cell

Blood in close-up

HAEMOGLOBIN

Haemoglobin is a pigment that gives
red blood cells their colour. It
contains iron, and it is very
special because it can make
temporary bonds with gas
molecules. Haemoglobin
combines with oxygen when red
blood cells travel through the
lungs. It gives up the oxygen in
other parts of the body, and
collects some carbon dioxide.

When it reaches the lungs once
more, it releases the carbon dioxide,
and the cycle starts again.

This computer-generated image shows a
molecule of haemoglobin. The pink parts are
the iron-containing groups that link with oxygen.

Thin layer of
white blood cells
and platelets

COMPOSITION OF BLOOD

If a sample of blood is spun around very quickly in a
test tube, the cells settle to the bottom. At the top is a
yellowish liquid, called the blood plasma. Plasma is
90 per cent water. The rest of it is mainly dissolved
food substances and salts, and also proteins such as
fibrinogen, which forms blood clots. Cells make up just
under half the blood’s volume, and red blood cells
usually outnumber white cells by 500 to 1.

In most people,
the plasma
makes up over
half the blood’s
volume.

Red blood cells
packed closely
together

A single drop of blood contains millions of cells. Most of
these are red blood cells, which contain a protein called
haemoglobin. This boosts the amount of oxygen that the blood
can carry by about 100 times. White blood cells are larger and
fewer in number. They engulf foreign cells (such as bacteria)
and attack intruders (such as viruses) by releasing antibodies.

The blood also contains cell fragments, called platelets, which
help it to form clots.

BLUE-BLOODED LOBSTER
Crustaceans, such as crabs and lobsters, and
some molluscs, use a pigment called
haemocyanin instead of haemoglobin,
substance gives their blood a blue
Haemocyanin contains copper colour. In crustaceans, haemocyanin is dissolved

instead of iron and, as shown in in the blood plasma, instead of being carried in

this Common lobster (Homarus blood cells,

vulgaris), makes blood blue not red.

BLOOD GROUPS
Blood is slightly different from one
person to another, because of special
proteins on the surface of its red cells
and in its plasma. People who have the
same proteins share the same blood
group. If blood f rom different groups is
mixed, the proteins can make red blood
cells stick together, which is dangerous.

So if someone has to have blood
replaced by a transfusion, the new
blood must be of the right group.

HOW BLOOD CLOTS

If you cut yourself, your blood eventually seals the wound. Blood
platelets near the wound become sticky, and they join together to
form a plug. While this is happening, a blood protein called
fibrinogen changes into fibrin. It makes a dense network of threads,
which contract and bind _

the red blood cells to
form a clot.

Cut skin releases
substances into the
blood. These make
platelets turn
sticky.

nuu

blood cell

The platelets join up
to form a plug. Fibrin
forms threads that
trap red blood cells.

Fibrin

threads

White blood cell

The fibrin and red blood cells form a clot,
which hardens to make a scab. When the
skin has healed, the scab falls off.

Find out more

Sep/

Cell

(

Inter

vRATING MIXTURES
\RTHROPODS P.322
ULAR RESPIRATION
^IRCUIATION P.34S
NAL ENVIRONMENT

P.61

)

p.346

p.350

348

HOW LIVING THINGS WORK

This artery takes
oxygen-rich blood
to the right side of
the head and the
right arm.

This artery supplies
oxygen-rich blood
to the left side of
the head.

Circulation

This vein carries
deoxygenated
blood from the
head, neck,
and arms.

This/
artery takes
deoxygenated
blood to the
right lung.

Right
atrium

This vein
brings
de¬
oxygenated
blood from
the lower
half of
the body
and the ’
legs.,

This artery takes
oxygen-rich blood
^ to the left arm.

This artery
takes
deoxygenated
blood to the
- left lung.

These veins
bring oxygen-
rich blood to
\ the heart.

Left atrium

Valves close as
the ventricle
contracts.

Left ventricle

The ventricles
have thick,
muscular walls.

Atrium

Right ventricle

Human heart

Your heart is like two pumps

working side by side. Each one is made of two muscular
parts: an atrium at the top, and a ventricle at the bottom.
During a heartbeat, the atrium contracts, and forces blood
into the ventricle. The ventricle contracts a split-second
later, forcing blood out of the heart and into the arteries.
The right side of the heart pumps blood from the body to
the lungs. The left side takes oxygen-rich blood from the
lungs and pumps it to the rest of the body. \

WILLIAM HARVEY

The Arab doctor Ibn
An-Nafls(c. 1205-88)
was the first person
to describe how
blood circulates
through the lungs,
but his work did not
become known in
Europe. It was not until
1628 that the English doctor
William Harvey (1578-1657)
published a full account of how the
blood circulates around the body.

He could not see capillaries, but he
deduced that they must exist.

Your HEART BEATS 100,000 times every day. It
squeezes your blood through a network of tubes
that take it on a journey around your body.
Humans have a “closed” circulation, which means
that our blood travels in special vessels all the way
round. When blood is pumped out of the heart, it
surges forwards under high pressure, which you
can feel as a pulse. Blood circulates at an amazing
speed: a single blood cell can take just one
minute to travel from your heart to your knee
and back to your heart. Simpler animals, such as
snails, have “open” circulations. Their blood flows
mainly through large body spaces, instead of
through narrow vessels. It is not pumped with
such pressure, and it moves quite slowly.

FISH CIRCUIATION
A fish has a heart with just two
chambers, and its blood flows
in a single loop. The blood
travels through the gills,
where it collects oxygen. It
then flows around the body to
deliver the oxygen and collect
carbon dioxide, which it then
takes back to the gills.

Lungs

Ventricle

BLOOD VESSELS

Your body contains about 100,000 km
(60,000 miles) of blood vessels. Arteries
take blood away from the heart, while veins
carry it back. Arteries and veins are linked
by a dense network of tiny capillaries, which
can only be seen through a microscope.
Capillaries form a network right through
your body.

FROG CIRCULATION
A frog’s heart has three chambers, two atria, and
one ventricle. Its blood flows in two loops - one
through the lungs to gain oxygen, and one around
the body to give up oxygen. When blood f rom both
loops returns to the heart, it becomes partly mixed.

Capillaries are the only
vessels whose walls are
thin enough to let
substances, such as
oxygen or hormones,
pass out of blood to the cells.

Arteries have muscular walls
and a tough outefi coating.

This helps them
to withstand high
pressures.

Veins have thin
walls, and vaives that
keep the blood flowing
in one direction.

Second
loop

HUMAN CIRCUIATION
Like all mammals and birds, we have a
double circulation. In the first loop of its
journey, the blood travels from the right half
of the heart through the lungs, gains oxygen,
and is bright red. On the second loop, it
travels from the left half of the heart, around
the body to lose oxygen, and gain
carbon dioxide; it is now a darker
red because it is deoxygenated.

Find out more

Inter

Breathing p.347
Blood p.348
NAL ENVIRONMENT

p.350

349

HOW LIVING THINGS WORK

Capillaries

Internal environment

The WORLD AROUND US is always changing. The air can get
warmer or colder, and it may pour with rain, or stay sunny and dry.
But inside your body, things stay much the same from one day to
another. The temperature is always about the same, and a constant
mixture of chemicals keeps your cells alive. This does not mean
that your body never changes. Instead, it makes tiny adjustments to
its internal environment all the time. Nerves and hormones
(chemical messengers) work together to keep your body in a
stable state. This process is called
homeostasis, and it happens
in all living things.

Excretion

All living things have to get
rid of waste. This is called
excretion. We excrete
carbon dioxide and water
through our lungs. We
excrete nitrogen
compounds, salts, and water
in our urine, and some salt
and water in sweat. We also
get rid of the undigested
parts of food - but this is not
true excretion, because
undigested food never passes
through our cells. Excretion
is important because waste
can poison the body. In a
healthy body, the nervous
system and hormones make
sure that waste products
never build up.

Crystals of
calcium
oxalate in
garlic (Allium
sativum

MONITORING THE BODY
Your brain is always monitoring the
internal environment of your body. A
part of the brain checks the amount of
carbon dioxide in your blood, and
increases your breathing rate if it is too
high. Other parts of your brain check
the water level in your blood, and your
body’s temperature.

Every time you breathe out, your
lungs give off carbon dioxide
and water vapour (this vapour
makes glass go misty if you
breathe on it).

EXCRETION
IN PI ANTS
Plants have to get rid of
waste, just like animals. During
photosynthesis, plants release waste oxygen
from their leaves. Some plants store solid
waste in their cells.The cells shown here are
from a clove of garlic. They have stored
crystals of calcium oxalate as a waste product.

Lizard basking
on a rock

“COLD-BLOODED” BODIES
Fish, amphibians, and reptiles are exothermic
(“cold-blooded”) animals. But their bodies
are not always cold. Instead, their temperature
rises and falls with the temperature of their
surroundings. Many exothermic animals alter their
body temperature through their behaviour. A lizard
will lie in the sun when it is cold, and it will hide in the
shade to cool down when it is too hot.

Your liver works like a filter and a
chemical factory. It removes worn-
out red blood cells, and stores the
iron that they contain. It also makes
sure that your blood contains the
right level of glucose, and it makes
the proteins that make blood clot.

Your kidneys filter your blood.
They drain off its fluid part as
it passes through them and
then make urine from the
waste that it contains.

Sweat helps to
cool you down.
It contains
salt, which
is why your
skin tastes
salty if you have
been sweating.

SHIVERING
If your body is too cold, your brain
sends signals to some of your
muscles to contract, or shiver. This
produces heat, which warms up your
body. At the same time, the blood
vessels near your skin become narrow.
This prevents too much of the body’s
heat escaping through your skin.

“WARM-BLOODED” BODIES
Mammals and birds are endothermic
(“warm-blooded”) animals. They can keep
their bodies at a set temperature,which is
usually warmer than their surroundings.
Endothermic animals can stay active even
when it is very cold, but their bodies need
lots of fuel to do this.

Sweat gland

Temperature regulation

Unless you are ill, your body temperature
stays at 37°C (98.6°F). Heat is produced by breaking down food
during cellular respiration. At the same time heat is lost. If you lose
more heat than you make, your brain signals your body to step up
your heat production, and prevents some heat escaping by shutting
off blood vessels near the skin, and making your body hair stand on
end. If you produce too much heat, you begin to sweat.

Muscle
lifts hair
upright.

This robin
(Erithacus
rubecula) has
fluffed up its
feathers to
keep warm.

Nerve

GOOSE PIMPLES
One of the first signs of feeling
cold are goose pimples - tiny
bumps on your skin. These
appear when tiny muscles lift
your body hairs upright.

350

IIOW LIVING THINGS WORK

The pituitary is a small but important gland just
under the floor of your brain. It produces many
hormones that stimulate other glands to
produce hormones of their own. The nearby
hypothalamus links your endocrine (hormonal)
system with your body’s nervous system.

The thyroid gland produces
thyroxine, a hormone that regulates
growth, and the rate at which
food is broken down to
release energy.

Hormones

Hormones are substances that carry a
message. In animals, they are made by
glands. A gland releases a hormone into
the bloodstream to travel around the body.
When it reaches the target cells, its message
is put into action. Your body produces more
than 50 different hormones. Some regulate
the levels of important substances in your
blood, and others control the way that you
grow and develop. They often work in pairs,
with each hormone having an opposing effect

(Vi

The pancreas
produces hormones
that control blood
sugar levels. The
hormone insulin
makes the cells use
more glucose and the
liver take glucose out
of the blood. The
hormone glucagon
makes the liver put
more glucose into
the blood.

High
blood
glucose

Insulin decreases the blood
glucose level, which triggers the
release of more glucagon.

Glucagon increases the blood

Low
blood
glucose

HORMONES IN PIANTS
If you put some seedlings on a
windowsill, they will bend towards
the light. This happens because
their growth is controlled by
hormones. Hormones gather on
the side of a stem that is away
from the light, making it bend.
Plant hormones mainly control
growth and development. Some
slow down a plant’s growth, and
others make leaves fall in autumn.

Honey bees (Apis mellifera)

FEEDBACK LOOPS

Insulin and glucagon are hormones that control the level
of glucose in blood. Insulin decreases the blood glucose
level, while glucagon increases it. The hormones form a
feedback loop, because each hormone affects what the
other one does.

L/\

Throughout the body, a
network of tubes called
the lymphatic system
drains fluid that seeps
{ N. out of the capillaries.
r The fluid, called lymph,
is filtered to remove
foreign cells and
, particles. The filtered
’ fluid then rejoins the
blood through a duct
near the heart.

Lymph nodes are spongy
swellings in your lymphatic
system, where white blood cells
attack germs. If your body is
infected by bacteria or poison,
such as from a snake bite, the
- lymph nodes often swell up.

CHEMICAL COMMUNICATION
Some animals release chemicals that send
messages to others. These chemicals are called
pheromones. Social insects, such as bees, ants,
and termites, pass pheromones to each other

through the air and by touching. A queen
bee controls a hive by making a special
substance containing pheromones.

MOBILE
DEFENCES
The white cells in
blood are the
body’s guards
against invasion.
One kind, called
phagocytes, are shown
here engulfing a string of
Streptococcus bacteria. They move through the
blood and body and engulf germs. Other
white blood cells, called lymphocytes, make
antibodies. These protein chemicals stick to
invaders and kill them.

~Your blood is one of
the most important

I .substances in

keeping your internal
environment stable.

It takes oxygen to the
cells, takes away
waste products, kills
harmful bacteria, and
carries all the
hormonal messages to
and from the cells.

Fighting disease

For microscopic organisms like
bacteria, your body is an ideal place to
live. It offers warmth and food. To stay
in a stable state, your body uses its
immune system to fight these germs. Your
blood and lymphatic system are very important
for doing this. Many of the germs that manage to get
into your body are engulfed by white blood cells.
Others are attacked by immune system proteins, called
antibodies. Once you have been attacked by a certain
bacterium, your immune system “remembers” its
chemical make-up, so it can respond very quickly to a
second attack. This is called immunity.

CLAUDE BERNARD

The French scientist Claude
Bernard (1813-78) was one of the
first people to study physiology,
which is the study of how all the
organs in the body work together
and keep the internal environment
stable. He discovered that
glucose, the main source
of energy for the body,
is stored in the liver as
glycogen, and released
as and when it is
needed. He also
studied digestion, how
drugs change the way
the body works, and
the nervous system.

Find out more

Bacteria p.313
Cellular respiration p.346
Blood p.348

Growth and development
p.362

Factfinder p.422

Queen bee

351

HOW LIVING THINGS WORK

The horseshoe crab has a domed shield that
covers its head. Its eyes are on top, and its
|? legs underneath. The crab has to moult
in order to grow.

A SKELETON SUPPORTS an animal’s body. It makes up
a framework that protects and keeps the body in shape, a
and gives its muscles something to pull against. Most p
familiar animals have skeletons that are made of
something hard, such as bone or shell. The larger an
animal is, the stronger the support system has to be.

Many small animals also have skeletons, but they are not »
always made from hard parts. An earthworm does not
have a single bone in its body, and instead it supports itself
by pressure from inside. Its body fluid presses against its skin
like air inside a tyre, making what is called a hydrostatic
skeleton; that is what allows it to burrow through earth. .

Abdomen

A millipede's body is made of
many segments. Each one
hinges with its neighbours so
f the millipede can bend.

Millipedes have to ^
hk moult to grow. ^ A

Exoskeletons

Many invertebrate animals have an ^

exoskeleton, which is a hard case that
supports their bodies from outside. In insects
and other arthropods, the exoskeleton is
made of stiff plates that meet at
flexible joints. The plates cannot iffi
change size once they have formed. 1^*^
To grow, an insect has to shed its
exoskeleton and make another one.

In beetles, the forewings have
evolved into a pair of hard plates,
or elytra. These cover the wings
underneath.

Unlike an insect or a
crustacean, a mussel does not
have to moult. Its shell gets
bigger with the rest of its body.

LIVING IN A CASE
An exoskeleton has several
advantages, and two important
drawbacks. It protects its owner from
injury, and it also makes it harder for
disease-causing organisms to attack. In land
animals, it also helps to stop the body drying
out. However, an exoskeleton can be heavy,
particularly on land. Some exoskeletons also
have to be moulted (shed) as their owners grow.
k During moulting, the exoskeleton splits and
the animal wriggles out of it, exposing a
new soft one underneath. Until this one
enlarges and hardens, the animal has to
hide as it is vulnerable to its predators.

These horns
are very hard
because they are
made of chitin.

Rhinoceros

beetle

Layers of chitin
laid on top of
each other.

CHITIN

Insect exoskeletons are made
from a substance called chitin.
This is laid down in layers of
parallel Fibres. The Fibres in the
different layers often run in
different directions, which makes
the exoskeleton very strong.

The joints are made of flexible tissue
so that the animal can move the
different sections of its body easily.

\ A beetle’s legs are covered
with hard chitin plates, like
I the rest of its body. The
I muscles that move its legs
are attached to the inside of
the plates in the next segment.

Muscle

Flexible joint/

Older shell
with more
turns

Spire of shell.

SUPPORT IN PLANTS

AND SINGLE-CELLED ORGANISMS

All plant cells are supported by cellulose,
but many of the cells in wood also have
a tough substance called lignin. Trees
stay upright because they have evolved
this very strong support material. In the
sea, single-celled diatoms make beautiful
. _ skeletons from silica, the same
mineral that sand is made
Spt °f* Each species of diatom
makes a skeleton in a
different shape.

Diatoms Pe

SHELLS

Molluscs have hard
exoskeletons, their

shells, which are JfM

made from the

mineral calcium JfmA

carbonate. As a 3

mollusc grows, it keeps ^BTy Jjf
laying down the mineral H
to the lip of its shell. This
gradually adds extra turns, so that the
space inside the shell gets bigger. By
enlarging its shell, a mollusc can keep the same
exoskeleton for the whole of its life. Unlike an
insect or a crustacean, it does not have to moult.

ijm

\ I'M

ill

Skeletons

I10W LIVING THINGS WORK

Endoskkletons

Like all vertebrates, humans have an endoskeleton -
a skeleton that supports the body from inside. Most
endoskeletons are made of bone and cartilage. Bone
provides the strength, while cartilage at the joints lets
bones slide over each other so that the body can move.
The human skeleton is made up of about 206
bones, ranging in size from the thighbone to
the tiny bones of the inner ear. Unlike an
insect’s body case, our skeleton grows in step 1 rj
with the rest of our body.

Cranium

(skull)

Mandible

(jawbone)

Suture line
where bones
meet

Forehead
bones fused
together

Clavicle (collarbone)

Scapula
(shoulder
* blade)

Humerus
(upper arm
bone)

JOINTS

The area where different bones meet is called a joint. Most
joints are movable, and in these the bones are covered with
a layer of cartilage. They slip over each other easily

because the cartilage is smooth and __

lubricated with a special __

fluid. The whole joint

is enclosed in a i N. /

tough membrane. 1 I \ /

mmm - FIXED JOINTS

Some joints are locked
together and cannot move. These are
found between the bones that protect
your brain, in your skull. When the
skull first forms, its bones are
separate. They gradually grow
together, forming wiggly lines called
suture lines. The two bones that make
your forehead join together
completely for added strength.

Vertebrae

(spine)

fSacrum
(base of
spine)

Pelvis

(hip

bone)

Radius (forearm bone)
Ulna (forearm bone)

Carpals
(wrist bones)
Phalanges
(finger bones)

HINGE JOINTS
Your elbow is a
hinge joint. It
can swing up and
down, but not
from side to side.

Coccyx

(tail

bone)

Pubic

bone

Femur

1 (thighbone)

BALL AND SOCKET JOINTS
Your hip and shoulder
\ joints can move in almost
\ any direction. Each one
\ contains a long bone

T \ that ends in a ball, and
‘ ~ - a socket that the ball
/ fits into. The two bones
/ are held together by
/ strong fibres called

/ ligaments.

Metacarpals
(hand bones)

Hard outer layer
of compact bone

Inner layer of
spongy bone
containing red
bone marrow

Patella

(kneecap)

Yellow bone
marrow
stores fat

- Tibia

(shinbone)

INSIDE A BONE
Bone is a living
tissue that

contains many types
of cells. Some of its cells surround
themselves with crystals of mineral
salts, and this makes the bone hard
and stiff. The inside of long bones
contains marrow, which makes
blood cells and stores fat.

Pectoral fin

Fibula
(calf bone)

SKELETONS M

WITHOUT BONES B

Human skeletons are
made entirely of cartilage
when they first form, in a
baby. The cartilage
gradually ossifies (turns into •

bone) until we are
about 25 years old.

Sharks and rays

have skeletons that

never ossify. Because

they live in water,

cartilage alone is strong

enough to support their bodies.

Tar sals
(ankle bones)

Metatarsals /
(foot bones)

_ .A snake's ribs do not go
right round the body on
the underside, so that
the skin on its belly can
stretch when the snake
n eats a huge meal.

Pelvic

girdle

(hips)

Cartilaginous
skeleton of a ray

Vertebrae

■psi, r 7 SKELETON WITHOUT LEGS

A snake’s skeleton is almost
entirely skull, spine, and ribs. It
contains hundreds of vertebrae (the
individual bones that make up the spine). A
snake can coil up its body because its spine
contains a huge number of joints, and each
can bend a little way. Snakes have no arm or
leg bones, and most snakes have also lost all
traces of their shoulder and hip bones as well.

Many of the bones in a snake's
skull are only loosely held
together. Its head changes
shape so that it can
swallow an

animal that SI

is larger

than its head. BjiLir.

Find out more

SlNGLE-CKI .1 .ED ORGANISMS
P.314

Arthropods p.322
Muscles p.355
Movement p.356

A snake’s spine
can bend back
on itself.

353

HOW LIVING THINGS WORK

_ Hair, nails, claws,
hooves, and feathers
are all made of the
protein keratin.

Muscle for
making your
hair stand
on end

SKIN COLOUR

Some animals can change the
colour of their skin. For example,
the cuttlefish changes its colour by
changing the size of special droplets
in its skin. Humans get their skin
colour mainly from a pigment
called melanin, which is made just
beneath the skin’s surface. Some
people also have carotene in their
dermis. So everyone’s skin is the
same except for the amount of
pigment it contains.

SKIN IS A TOUGH, FLEXIBLE COVERING that protects your body, and
helps to keep it at the right temperature. Although it feels alive, its outer
surface is completely dead. Without this dead layer, your body would soon
dry out or be invaded by bacteria. Your skin renews its outer surface all the
time, and quickly repairs itself when it gets cut or scratched. If part of your
skin, such as the soles of your feet, gets more wear than normal, it gets
thicker. Most of your skin is covered with hair, but most mammals have much
more hair. Your skin is very good at cooling you down. If you are hot, the
capillaries in your skin fill with blood so that heat is lost to the air, and you
sweat, which cools you down when the sweat evaporates. Skin is your
largest organ; in an adult it covers about 2 sq m (21 sq ft).

Inside the skin

Skin is made of two layers, the epidermis
and the dermis. The epidermis is the outer
layer. At its base is a single layer of cells
that divide all the time. As the new cells
are pushed upwards they die, forming a
tough layer on the surface. The dermis is
the lower layer and is much thicker. It
contains elastic fibres that make the
skin stretchy. It also has hair
follicles, blood vessels,
sensitive nerve endings,
fat, and sweat glands.

Sweat glands send sweat
to the surface of your
skin through little
holes called pores.

Section through
human skin

Cells containing fat form a
layer that helps to keep
the body warm.

Sebaceous
(oil) gland

Epidermis

Single layer of
dividing cells

Dermis

follicle

FEEDING ON SKIN
Even- day, people shed millions
of dead cells from the surface
of their skin. These cells are
found in house dust, and they
provide food for tiny house dust
mites. The mites are usually
harmless, but some people can
be allergic to their droppings.

Surface cells gradually
wear away, but are
replaced by new cells
from below. Each cell
lasts about four weeks.

Dead layer about
25 cells deep

Nerves

Blood

vessel

This capillary
widens when
you blush or
do lots of
exercise.

Sweat

gland

WRINKLES
If you pinch
your skin and
let go, it springs
back into shape.

This happens
because skin
contains proteins in
the dermis that stretch
like elastic. As people get
older, their skin becomes less
elastic, so it begins to form wrinkles.

Overlapping scales slide
against each other, so
the fish's skin is still
flexible in spite of
this hard covering.

FINGERPRINTS
The skin on the palms of
: your hands and the soles
of your feet has tiny ridges.
These give your skin a
better grip for holding on
to things. Every person has
their own unique pattern of
ridges. The pattern gets
bigger as you grow, but it does
not change shape.

SCALES

Most fish are covered in
overlapping scales to
protect their skin. They
grow out from the dermis,
and are made from bone
and other tissues. Most
bony fish have round
scales that make them shiny
and smooth, while sharks have
small pointed scales that give
their skin a sandpapery texture.

Find out more

IlFAT TRANSFER P.1'12
Molluscs P.32'1
Fish p.326
Reptiles p.330
Birds p.332

Internal environment p.350

Skin

354

HOW LIVING THINGS WORK

Muscles

on the back of*
the frog’s thigh
make the leg
extend.

Muscles on th
back of the lower

Powerful

muscles in the ^
frog's hindlegs give
it the power to jump.

A tough membrane

HUMAN MUSCLES

The human body contains about 660 voluntary
muscles (muscles you can move when you want
to). They have a rich blood supply, which
provides them with oxygen and glucose. Muscles
get warm when they contract, and they supply
about f'our-fifths of vour bodv’s heat.

Very few
movements take
just one pair of
muscles. Most
involve several
muscles working
together. For
example, to
swallow you
use at least
six muscles.

When you lower
your arm, your
biceps muscle
relaxes. If you now
try to make your
arm as straight as
possible, you can
feel your triceps
tighten up.

Triceps

A human
voluntary
muscle

Myofibril

Muscle

When
you raise
your arm,
your biceps
contracts. The
opposing muscle
- the triceps
relaxes.

Triceps

LUIGI GALVANI

By accident, the
Italian Professor of
Anatomy Luigi
Galvani (1737-98)
discovered that a
dead frog’s legs
contracted if they
were pegged to an
iron frame with brass
pins. Galvani thought
that frogs’ muscles
made electricity, which
caused the contractions. Galvani
was right to think that electricity
made the muscles move, but in
fact it was the two metals reacting
together that made the electricity.
We now know that in living
animals, electrical signals from
nerves make muscles contract.

ABOUT HALF THE WEIGHT of your body is taken up by muscles.
They make your body move. Muscles can pull, but they cannot push.
To make up for this, most of your muscles are arranged in pairs or
groups, so that they pull in opposite directions. Vertebrates (animals
with backbones) have three different types of muscles. Voluntary or
skeletal muscles are attached to your bones by tough tendons, and
when they contract, part of your body moves. These muscles are
easy to feel, because you can make them move whenever you want
to. You also have other muscles that work automatically. These are
called involuntary or smooth muscles. They squeeze food through
your digestive tract, for example. A third kind of muscle is found
only in your heart. Cardiac or heart muscle contracts
automatically, and never gets tired.

Making a move

When a frog jumps, signals flash from its brain through its
nerves to the muscles in its legs. The signals cross from
the nerves to the muscle fibres, and the fibres
contract. Even when the frog is not moving,
some of its muscle fibres contract while
others relax. This makes each muscle
firm (toned) which keeps the
frog’s body in shape. Muscle
tone is important in our
bodies as well, and
it is improved
by regular

^ exercise.

Bundle of
fibres

MUSCLE
STRUCTURE
A muscle is made of
lots of fibres arranged in
bundles. Each fibre is a single cell.

The cells are unusual because they
have many nuclei, and can be more
than 1 cm (*/2 in) long. The
fibres (cells) are made of
even smaller filaments,
called myofibrils. These
contain chemicals that slide
past each other and make
the muscle contract.

covers and protects

the muscle. Acf/n filament

Rough

limpet

(Collisella

seabla)

Relaxed

myofibril

Contracted

myofibril

Myosin filament

HOW A MUSCLE CONTRACTS
A myofibril contains bunches of two
proteins, actin and myosin. Each one
is made of separate filaments, and
these are packed in overlapping layers.
When the myofibril is relaxed, the
actin and myosin filaments overlap
slightly. If the myofibril is triggered by
an electric signal from a nerve, the
myosin filaments are attracted to the
actin filaments, and they slide past
each other. The myofibril shortens,
and so the muscle contracts.

LOCKING SHUT
If you lift a heavy weight, your
arms will quickly get tired. But
af ter .the muscle in a limpet’s
foot contracts, it locks in
position. Once locked, it does
not need any more energy to
stay contracted, although it
does need energy to unlock. This
is a special sort of voluntary
muscle called catch muscle.

Find out more

Cells and batteries p.150
Molluscs p.324
Amphibians p.328
Cells p.338
Circulation p.349
Movement p.356
Nerxts p.360

355

HOW LIVING THINGS WORK

Movement

The cheetah (Acinonyx jubatus) is the
fastest land animal. It can reach a
speed of about 110 km/h (70 mph) by
taking enormous strides up to 7 m (23 ft) long.

spread out almost horizontally and its
spine curves downwards. Its skeleton
is unusually flexible.

The cheetah’stall
swings up and down
to balance the
movement of its legs.

MOVING WITHOUT LEGS

Snakes move by four different methods. In the most common way, a snake curves its
body. This is called serpentine motion. Each curve pushes against the ground so that
the snake slides forwards. In tight spaces, a snake anchors its tail, and then stretches
forwards. Its tail then catches up in a concertina motion. Heavy snakes creep along in a
straight line, by raising and lowering their belly scales. This is called rectilinear motion.
Some snakes throw themselves forwards in a special movement called sidewinding.

This common garter snake
(Thamnopis sirtalis) is
moving along using
serpentine motion.

The cheetah’s spine
curves upwards so that
its back legs can come as
far forwards as possible,
ready for the next leap.

Even when you sit very still, parts of your body are

moving. Your heart beats to send blood around your body,
and food is moved through your digestive system. This is
involuntary movement, because you do it without thinking
about it. Like most animals, you use voluntary movement to
move part of your body, or carry your entire body from place
to place. Moving your whole body from one place to another
is called locomotion. The way an animal moves about depends
on the shape of its body, its surroundings, and its size. Small
animals generate more power in proportion to their weight,
so in relative terms, they move faster than large ones. If a
cockroach was as large as a human, and its speed was scaled
up in proportion, it would race along at 140 km/h (85 mph).

MOVEMENT IN PLANTS

Some plants, such as daisies, open
their flowers when the Sun rises, and
close them when it sets. This is known
as sleep movement, and happens
because of pressure
changes inside the
plants’ cells. Leaf¬
folding is another
common form of
sleep movement.
It happens, for
example, in
clovers and other
members of the
pea family.

Muscles contract
to tighten the
oesophagus and
move the food.

Food

Peristalsis happens in reverse
when the stomach rejects food.
When this happens, you vomit.

Moving on legs

A wink is a conscious movement that is relatively
slow. Blinking is a very fast automatic
movement that cleans your eyeballs.

FACIAL EXPRESSIONS
Facial expressions, such as looking
shocked, or smiling, are tiny voluntary
movements made by more than 30 different
muscles. Although they are voluntary,
you often make these movements
with hardly any thought.

Animals with legs have to move them in a carefully co-ordinated way.
We move our legs alternately. A walking cheetah moves its front
right leg and back left leg together, then the opposite pair. When
it is running at top speed, it moves its front legs together and
then its back legs together.

ELASTIC POWER
A Ilea can leap over 100
times its own height
because of tiny pads of
resilin, a rubber-like
protein that stores
energy. The pads are in
the joints between the
Ilea’s legs and its body.
Before each leap, energy
from the Ilea’s contracted
muscles is stored in the pads. As
the flea jumps, this energy is
instantly released, causing its legs to
flick back suddenly, throwing the
flea into the air.

PERISTALSIS
When you swallow, muscles at the back
of your mouth contract to push food
down your oesophagus. This movement,
called peristalsis, carries food through
the whole of your digestive system. You
decide when to swallow, but after that
your food is moved by automatic
peristalsis - an involuntary movement.

Daisies (Beilis perennis) closing
their flowers as the Sun goes down.

SNAIL TRAIL
Snails and slugs have a single sucker-like foot.
The foot is made of muscle, which contracts in
waves to allow the animal to creep forwards.
Mucus (slime) enables a snail to grip and move
over rough surfaces.

356

HOW LIVING THINGS WORK

Albatross

Lift pushes
upwards

Gravity pulls
downwards

Flying and swimming

Flying and swimming are ways of moving through
two quite different fluids. Animals fly and swim by
pushing backwards. A force called reaction acts in
the opposite direction, so that they travel forwards.
The bodies of most swimming animals are as dense
1 as the water around them, so they do not rise or
sink. Flying animals have bodies that are far
denser than air. They have to use their wings for
staying up, as well as for moving along.

GLIDING FLIGHT

A bird’s wing has an “aerofoil” shape, which means that it
lif ts upwards when air flows over it. When a bird glides,
gravity pulls it downwards, but lift opposes the downward
force. Birds use gliding flight to cover long distances with
little effort, especially in warm rising air.

STEERING IN THE AIR

Many flying insects have two pairs of wings. Craneflies
and house flies have just one pair. Their hindwings have
evolved into tiny club-shaped organs
called halteres. The halteres vibrate
as the insect flies, and they
produce nerve signals that keep
the insect on course.

Halteres help
this cranefly keep
its balance as it
flies along.

5. The
wings are ready
to be pulled down
again by powerful
muscles in the bird’s chest.

FLAPPING FLIGHT
A bird flaps its wings to
push itself through the
air. As it moves forwards,
the air flowing over its
wings creates lift, which
holds the bird up. If the
bird stops flapping, it
slows down. The lift
decreases, so it begins to
drop. Birds use flapping
flight to travel at speed
or in a set direction.

4. The wings
begin to move
up once again. Lift
counteracts gravity, so
the bird stays up as its
flies along.

A dogfish uses its
pectoral (front) fins to
alter the angle of its
body as it

3. During
the downstroke,
the wings push down and
backwards against the air.
Reaction makes the bird move up
and forwards.

Pelvic fin

Tail fin

SWIMMING
A fish swims by pushing
against the water with its
Fins or with its whole body.

Most cartilaginous fish,
such as this dogfish, bend
their bodies as they swim,
but bony fish, such as a
goldfish, often propel
themselves just with their tail or
pectoral fins. They use their other fins
for steering. Fish such as tuna and
mackerel have special groups of muscles
that are used f or bursts of speed.

MOVING BY HAIRS
Sea gooseberries, also called comb
jellies, do not have any legs or fins.
Instead, they move by beating tiny
hairs, called cilia. The cilia are
arranged in clusters that work like
paddles. A sea gooseberry uses its
cilia to stay the right way up, and to
keep near the sea’s surface.

STAYING IN ONE PLACE
Barnacles are marine animals that glue
themselves to hard surfaces. They feed by
beating their feathery legs, and collecting
any food that becomes trapped in them.
Barnacles spend their entire adult lives in
one place. Like all sessile animals
(animals that are fixed in one place),
their larvae can swim or drift from one
place to another.

1. A swimming dogfish contracts
the muscles on either side of its
body in turn. This makes its body
curve from side to side.

Swimming

JET PROPULSION
A squid’s body contains a cavity
that is normally filled with
water. The squid can make the
cavity contract very rapidly, so
that the water squirts outwards
through a tube called a siphon.
The force of the moving water
pushes the squid in the opposite
direction. The squid changes
direction by altering the
position of its siphon. Cuttlefish
and octopuses also move by this
kind of jet propulsion.

1. The wood pigeon’s
streamlined body
reduces its friction with
the air as it flies along.

2. During
the upstroke,
the bird raises
its wings so
that they
almost touch.

2. The
dogfish's tail
and body push
water backwards.
A reaction force
pushes it forwards.

The cilia on a sea
gooseberry's body are
for locomotion. The cilia
on its tentacles help it
catch food particles.

Find out more

Speed p. 118

Forces and motion p.120
Molluscs p.324
Fish p.326
Reptiles p.330
Birds p.332
Digestion p.345
Muscles p.355

357

1I0W LIVING THINGS WORK

Senses

ALL THE SENSES
People often refer to the five
senses, but yon have many more
than this. Touch is actually
several senses. Special neive
endings in your skin detect
pressure, pain, heat, and cold.
You can feel where your arms
and legs are, and your sense of
balance helps you stay upright.

Lateral
line on the
side of a
rudd

If YOU HAVE EVER TRIED to find a friend who is hiding, you will know
how important your senses are. If your friend makes just one accidental
sound, or moves something, it will be enough to let you know where she is.
Senses keep us in touch with our surroundings, and also with our bodies.
Sense organs like eyes and ears send a stream of information along nerves to
the brain. The brain sorts out the signals, and then makes the body react to
them. Different animals rely on different senses according to their way of life.
Some, such as cats, have very good eyesight and hearing; others, such as dogs,
have a strong sense of smell.

Some animals find out about whiskers

When there is no light to see by, you may walk
with your arms out in front to feel your way.

Other animals, such as this crested
porcupine (/ lyslerix africamus(mlis) , feel
with their whiskers. These are long stiff
hairs on an animal’s head. They will
brush against anything in the way
I 1 i I before the animal bumps into it.

their surroundings by
detecting pressure, heat,
or even electricity.

LATER AL LINE
Many fish have a line of sensors
along their sides, called a
lateral line. These sensors
detect waves of pressure
travelling through the water.

A fish’s lateral line enables it
to feel the movement of
other animals around it.

Sensing movement and pressure

Many sense organs detect movement and pressure, which
includes touch, sound, and vibrations. Most of a grasshopper’s
body is sensitive to touch. Its body also has cells that detect
vibrations in the ground, and these warn it to hop out
of the way when another animal approaches. Sound
is another form of pressure, and the
grasshopper detects this
through its ears.

Ear bones

A grasshopper's
eardrums can be on the sides
of its abdomen, or on the
lower part of its legs.

Antennae are
sensitive to touch
and chemicals in
the air

SENSING LIGHT
A grasshopper has
compound eyes. These are
eyes which are divided up
into many facets (simple
eyes), each with its own lens.

Each facet has a lens, and it
forms a tiny image.
The grasshopper
combines these
images to see the
world around it.
Our eyes work in
a different way.
They each have just
one lens. The lens focuses
light onto a curved screen of
light-sensitive nerve cells,
forming just one image.

Sensitive cells around joints
between body plates

BODY SENSORS

The hard plates around a grasshopper’s
body are linked by flexible joints. Each
joint has special cells on either side, which
are either squashed or stretched,
depending on the joint’s position. The
cells send signals to the grasshopper’s
brain, and from these signals the animal
can sense the way the body is positioned.
Like nearly all animals, a grasshopper also
has other cells that detect the pull of
gravity. This tells it which way up it is.

SENSING SOUND
A grasshopper’s ear is a flat
drum on its body case, with an air-
filled space behind it. Sound waves
vibrate the drum. Gells attached to
the drum sense the vibration, and
send signals to the brain. Small
insects, such as midges and
mosquitoes, can detect sound with
their antennae.

Middle ear

Cochlea

Outer

ear

Your semi-circular
canals help you to
keep your

Inner ear

HUMAN EAR

Your outer ear
channels sound waves
into the eardrum,
making it vibrate.
Three tiny bones in
the middle ear carry
the movement to the
cochlea. This contains a
fluid and cells with
special hairs. The vibrations
travel through the fluid, and
make the hairs move. This triggers
nerve cells, which send signals to your
brain. The brain sorts the signals into
sounds that you hear.

358

HOW LIVING THINGS WORK

Taste and smell

Animals use the senses of taste and smell to detect
chemicals. When you taste something, groups of
cells on your tongue, called taste-buds, detect
k chemicals dissolved in your saliva. When you
smell something, cells at the top of your nose
■ detect chemicals dissolved in the moist

lining of your nose. Taste-buds detect only <
HI what we describe as sweet, sour, salt, and
E/ bitter. Flavours are combinations of
r these four, so they are much
more varied. Taste is linked to

the sense of smell, which fe.

is why it is hard to tell .%.■_/ T": .•

jfjjL different foods apart if
your nose is blocked.

Adder

(Vipera berus)

SMELL |

Some animals use scents
to send and receive
messages. For example, \

dogs leave their scent to
mark their territory, or to
let other dogs know they
are around. Dogs
use their sense of
smell to build up a “picture”
of the world around them.

JACOBSON’S ORGAN L/

A snake detects different 1/

smells in a pit in the roof r"*
of its mouth called a t , 7

Jacobson’s organ. The \

snake flicks out its tongue to \
collect chemicals from the air,
then presses the forked tip into
the Jacobson’s organ. Special cells
lining the pit detect the chemicals
picked up from the air.

Ag taste

Different taste-
mm buds on an

animal’s tongue

detect

such as sweet or sour. .An
animal’s sense of taste enables it to tell if something is
good or bad to cat. Animals use this sense to choose
fpod to eat, and to avoid eating something poisonous.

Jacobson's

organ

Most taste-buds lie in
tiny grooves in the
surface of the tongue.

PLANT SENSES

Plants do not have special sense
organs, but they can respond to the
world around them. All plants detect
light and gravity, and some plants also
sense nearby objects. The sensitive
plant (Mimosa pudica) has very quick
reactions. Its leaves go limp if they are
touched. The
tendrils of
climbing plants
can “feel” things I
that they touch.

They respond by H ' '
coiling up, to

attach the plant *

to a support.

JUDGING DISTANCES

Many animals, including humans, have “binocular
vision” which allows them to judge distances. Binocular
vision means having two eyes facing forwards, which
gives two slightly different views of the same object.

The tiny jumping spider (Lyssommies viiidis) has four
pairs oflarge eyes. Some of its eyes point sideways, but
one pair looks directly forwards. This pair of eyes
enables the spider to judge how far away its prey is
before it jumps on to it.

ELECTRIC FIELDS
In muddy water it is difficult to see.
Some fish, such as this Gymnarchiis
niloticus use an electric field,
produced by special muscles, to
detect things nearby. If something
disturbs the field, the fish can tell
what it is by the size and position of
the disturbance.

A male cockchafer’s
antennae unfold like fans.

Tendrils of
climbing plants,
such as this
pea plant, are
modified
leaves.

FINDING A MATE
Female insects often let male
t insects know where they are
I by releasing tiny amounts of
chemicals called pheromones
k which spread through the
% air. These are detected by a
m male of the same species,
f which then follows the

pheromone trail to track
down the female in order to
mate. The male cockchafer
(.Melolontha mdolonthn ) detects
the female’s pheromones with
its f eatherv antennae.

Find out more

The folding leaves of
the sensitive plant may
help the plant escape
being eaten.

Making and i imaking
SOUND P.182
Vision p.204
Ar n IROPODS P.322
Fish p.326
Skin p.354
Movement p.356
Nerves p.360
Brains p.361

359

HOW LIVING THINGS WORK

1. Pain triggers the
sensory neuron to
produce a signal.

If you hurt yourself,
the signals travel to
your spinal cord
4^-and not your brain,

r _ for the quickest

*9? possible reaction.

WHEN YOU PICK UP this book, lots of things happen very
quickly. Your arms adjust to the book’s weight, so that they
lift it with just the right force. Muscles in your back contract,
so that you do not tip forwards, and the lenses in your eyes
change shape, so that your eyes focus on the pages. Thanks
to your nerves, you are now ready to read. Nerves are
bundles of long, thin cells called neurons which carry
fast-moving electrical signals. The sensory neu
carry signals from different parts of your body
your brain or spinal cord. The motor neurons
carry signals from your brain or spinal cord to
your muscles to make them contract. Between
them are different neurons: the association
neurons, which pass signals to motor
neurons, and send messages to your brain.

v How

NERVES WORK
You have three types of
/rfP 1 neuron (nerve cell) in your
body. If you touch something
HijHfflFthat hurts, the pain is detected
by a sensory neuron. This
/ flashes a signal to an association
/ neuron in your spinal cord. This
IIP neuron then passes the signal to
N one or more motor neurons, and
r these make you move. This kind of
split-second reaction is called a reflex.

J// 7 5. A

m/ / motor
y.U' neuron
H[\ makes
/ J muscles
A, /contract,
y pulling
// y your hand A
/ /' away from K
y the source
of the pain. / VC

(// / / 2. The

/Ta''" signal races
/ //) along the

/ // / neuron's axon

/■// (fibre). Axons are
'7/Z / much thinner than
y J a hair, but they can
Z be very long. Some
run all the way along
your arms or legs. //

Myelin

sheath

MYELIN

Some neurons are covered by a fatty
substance called myelin. This helps to
make the nerve signals travel faster. It
also works like the plastic insulation
around a wire, so that the neuron’s
electric signal does not leak away.

The myelin is made by special
cells which wrap themselves
around the axon many times.

HUMAN NERVOUS SYSTEM
Your nervous system consists of the
central nervous system (spinal cord
and brain), and the peripheral nerves.
Your brain co-ordinates almost
everything that your body does. J
Some of your nervous system is
under your control. The rest
works automatically, so that your /))
body runs smoothly without you j/j

telling it what to do.

4. The association
neuron passes the
signal across a
synapse to
a motor
neuron.

/Z!fZ) NERVE NETS

f ////fi// A flat worm’s
//'// / nerves are scattered
| //W across its body in an
jZZ interconnecting net.

' / The nerves produce
W signals which make its
f body contract in
waves, so that
it swims. ., A r

.... Nervous
system of
flat worm

Cell body
of sensory
neuron

V 3. The signal is association
passed to an neuron by
association neuron jumping across
in the spinal cord, a synapse.

Ganglia

< -- 1 . Candystripe
flatworm
-^Prostheceraeus
vittatus)

^NERVES IN INSECTS
The nervous system of an
insect is simpler than ours.
Jt consists of a brain and
clusters of neurons, known
ks ganglia. These are joined
rows of nerve fibres.

Cell body /
of association
neuron

Cell body of
motor neuron

Nervous ^

pflP jt system of a

-^Grasshopper W grasshopper

GIANT NERVES _

An earthworm has special giant
neurons that run from its tail to
its head. These cells carry signals
about 50 times f aster than the rest
of its nerves. If a bird pecks at a
worm’s tail, signals race along the
giant nerves and make the worm
contract almost instantly. _

SYNAPSES X

Neurons meet at /

tiny gaps, called / //

synapses. Nerve ll I

signals jump across X

the gap in one \

direction. Some \ ^

neurons pass on a signal
as soon as they receive it.

Others wait for a number of signals to
arrive before sending one of their own.

Find out more

Worms p.321
Arthropods p.322
Internal environment p.350
Muscles p.355
Senses p.358
Brains p.361

360

1I0W LIVING THINGS WORK

View of the left half
of the human brain,
seen from inside

Area used to
move body

White matter, made
up of nerve fibres

Area used to

Brains

Grey matter,
or cortex

Area used to

interpret

sensations

Front

Back

Area

used

vision

Cerebellum
co-ordinates
muscles, and
controls posture.

Spinal cord

gland
Brain stem controls
vital functions
including breathing
and circulation.

Your BRAIN IS IN TOUCH with the rest of your body all
the time. It contains billions of neurons (nerve cells) that
link up with each other, and with all of the nerves in
your body. Scientists know a lot about individual
neurons, but the way that the whole brain works is
not fully understood. Experts are only just
beginning to discover how we think or how we
remember things. But it is known that our
brains are divided up into separate areas.
Some areas deal with the general running of
the body. Others are involved in co-ordinating
our movements, or understanding spoken words.
While you are awake, you are conscious, or aware
of what you are doing. When you fall asleep,
your conscious brain shuts down, but other parts
continue the essential work of keeping you alive.

Frontal
lobe of
cerebrum is
involved in
conscious
thought.

BRAIN CELLS
The nerve cells in the brain can
have synapses with over 200,000
neighbouring cells. Signals from
their neighbours may either make a
group of cells send a message (like
making you swallow), or prevent
them from doing so (like taking a
breath while you are swallowing).

Cerebrum
(part of
forebrain)

Optic lobe

Cerebellum

Human brain

Your brain is divided into three main regions.

Two of them, the brain stem and cerebellum,
look after the running of your body. They
control your breathing, your circulation, and
your posture. The cerebrum, which is
much larger, processes information. It is
this part of your brain that you use to
think. Your brain contains about 1,000
billion nerve cells when you are born.

This number slowly decreases as
you get older, because neurons
die and cannot be replaced.

H Pituitary gland, BIRD BRAIN

Cerebrum . In a bird’s brain, the cerebrum does not

(part of P* 10 0 6 _ cover the cerebellum. The brain has a large

r , . v _ Cerebellum • , , , ,

forebram)_ __ _ optic lobe - the part that processes

information from its eyes.

Forebrain

Brain stem

FROG BRAIN
A frog’s cerebrum is quite
small, while its cerebellum is tiny. Its brain stem
makes up about half of the brain’s volume.
Vision is important to a frog because it hunts by
sight. I ts optic lobes are not as large as a bird’s,
but they are still a major part of its brain.

IVAN PAVLOV

Pavlov (1849-1936)
was a Russian
physiologist who
investigated the way
reflexes work. He knew
that all animals have
inbuilt reflexes, but he found that
new reflexes could be conditioned
(learned). Pavlov conditioned dogs
to expect food after a bell was
rung. He found that their new
reflex made them salivate (drool)
after the bell sounded, even if
there was no food.

Brain

stem

Co-ordinating
area of brain

Nerves to arms and

These large
lobes deal with
nerve signals

from the eyes. I M l IMF Nerves

to body

INSTINCT AND LEARNING
A male great bower bird (Chlamydera
nuchalis) builds an extraordinary
bower (an alleyway) out of sticks, and
decorates it with bright objects. If he
is lucky, it will attract a mate for him.

The male bower bird does not have
to learn how to do this complicated
work. Instead he does it by instinct.
Instinct is a kind of behaviour that
is inherited, rather than learned.

OCTOPUS BRAIN
An octopus has one of the largest
brains of all invertebrates. It is
built on a completely different
plan from the brains of
vertebrates, and has many
connected lobes. Octopuses have
good eyesight, and a large part of
their brain deals with signals
from their eyes. Experiments
have found that octopuses are
intelligent animals. They can
work out how to reach food, even
if this means taking the stopper
out of a submerged bottle.

Find out more

Molluscs p.324
Amphibians p.328
Birds p.332
Senses p.358
Nerves p.360

361

HOW LIVING THINGS WORK

Growth and development

Most living things get bigger as they get older. They do not do

this by having bigger cells, but by making more of them. When a cell gets to a
certain size, it makes a copy of itself to make two new cells. The two new cells
can also divide, and so many cells build up. This is cell division.

Some living things, such as plants, carry on
growing by cell division all their lives.
But in most animals, including
humans, cells divide more slowly
once the adult body has
taken shape.

/ > Half-

V ^ V chromosome

4. Each chromosome starts
to separate into two identical
halves, pulled apart by the
spindle which is attached to
the centromere. The halves
move towards opposite ends
of the cell.

1. For most of the time, in the
periods between cell divisions,
a cell's DNA (deoxyribonucleic
acid) in the nucleus is spread
out and too thin to see.

Spindle

Nucleus

Spindle

Chromosomes

2. The DNA copies itself and coils up
into chromosomes. The chromosome
and its copy are held together by a
centromere. Tiny chemical threads,
called the spindle, begin to take shape.

Cell

membrane

3. The membrane around the nucleus
disappears. The spindle is now fully
formed, and the chromosomes start to
line up in its centre.

Cell division

Before a cell can divide, it must duplicate its
chromosomes (the thread-like structures that
contain DNA). The duplicated chromosomes ar
then pulled apart and two new nuclei are made.
This is called mitosis. When mitosis is complete,
the cell divides, so that two identical cells
are made. This kind of cell division is /
used for growth. Another kind of /
division, called meiosis, occurs / A

before sexual reproduction. It does 1

not make identical cells.

5. A membrane
forms around
each set of
chromosomes,
creating two
new nuclei .^h

DIVISION IN ACTION
In this thin layer of cells from an
onion root, each cell is
surrounded by a cell wall. The
dividing cells have clearly visible
chromosomes. In the other
cells, the chromosomes are
spread out in the nucleus. Plant
and animal cells divide in a very
similar way, although plant cells
have to make a cellulose cell
wall after thev are formed.

6. A furrow starts to
form around the cell.

As the furrow deepens,
the cytoplasm is
pinched into
two halves.

7. The two new cells
are now complete.

Each contains exactly
the same DNA as its
parent cell, and as
each other. These cells
can now duplicate
themselves to
produce four cells.

8. After division
is complete, the
DNA in the
chromosomes
spreads out again.

GROWTH IN TREES
A tree grows in two different
ways. Cells at the tips of its
branches and roots divide so
that the branches and roots
grow longer. At the same time,
cells just underneath the bark,
called the cambium, divide to make
the trunk and branches thicker.

CELL CYCLE

Many of the cells in your body divide
according to a fixed timetable. A cell inside
your cheek, for example, divides about
once every 24 hours. Not all cells divide
this quickly. In some cells, division is
“switched off” during a long gap period. In
nerve cells, division stops altogether after
the cell is formed in a baby in the womb.

period (4 hours) and cel1

-cell grows division

and prepares to
divide.

3. Synthesis
period (9 hours)

- chromosomes
are duplicated.

Division cycle of a cell from the inside of a cheek

0 . Growth

rings are
formed by a
burst of
growth every
spring, slower
growth in summer,
and none in winter.

SEEDLINGS A

^ Growth needs lots of
energy. A seedling can grow
quickly because it has a
store of food in a tissue
in the seed called the
endosperm. Sometimes the seed-
leaves (cotyledons) also have a
store of food. In many
seedlings, the cotyledons
quickly open up so that ^

photosynthesis can begin.

2. First gap
period
(10 hours).

As a sapling grows, its lowest
branches drop off to leave a bare
trunk. The trunk thickens but does
not stretch upwards - an old
branch scar will always
* " stay at the same height.

Food stored in
the seed gives it
the energy to
germinate.

362

HOW LIVING THINGS WORK

Find out more

Fix:

Starfij

Inter:

IWERING PLANTS P.:
Vrthrofods p.322
>H AND SEA SQUIRT
Cells p.338
SAI. ENVIRONMENT
Genetics p.364

318

s p.325

p.350

An adult crab has a short tail, which is
folded up underneath its body. It
has strong legs, but is not a good
swimmer. This is a shore crab
(Carcinus maenas).

COMPLETE METAMORPHOSIS
A crab changes shape completely as it grows up. It
starts life as a tiny zoea larva, which floats in the
upper waters of the sea. After moulting its body
case several times, the zoea turns into a megalopa
larva, which can walk as well as swim. Finally, the
megalopa moults and becomes a voung crab.

Growing up

The cells in your body do not all divide at the same rate. As
you grow up, many of your cells, particularly those in your
arms and legs, divide faster than those in your head. As a
result, your body slowly changes shape. This is development.
Growth and development are controlled by hormones -
chemical messengers which are carried by your
blood to the different parts of your body.

Some of these hormones make your body
put on a sudden burst of growth from the
age of about 12 or 13, and
make you stop growing
altogether at around 21.

Human development

GROWING MISSING PARTS

If you cut yourself, cells in your
skin start to divide until the cut has
healed. This kind of growth is
called regeneration. We can
regenerate skin and bone, but
some animals can regenerate entire
parts of themselves, including legs
and tails.

Starfish can grow

a new leg if one

Inside a chrysalis,
most of a

caterpillar's cells are
broken down. New
cells then form the
butterfly.

By the age of five, the
arm and leg muscles
have got much
stronger. A five-year-
old can walk and run.

A 10-year-old has longer
limbs, and has learned
how to make precise
movements, such as
writing, or catching a ball.

At the age of 13, many
changes are taking
place in the body. It is
growing quickly, and
preparing for adulthood.

Most 20-year-olds are fully
grown. The head is now a
smaller part of the body. The
wisdom teeth are one of the
last parts to finish growing.

INCOMPLETE METAMORPHOSIS
A bug gradually changes shape as it grows up. When it
hatches, it has no wings or reproductive organs. As it
grows up, it moults (sheds its case). After each moult,
its body changes slightly, and after the fif th moult it
becomes an adult. This slow change of body shape is
called incomplete metamorphosis. Cockroaches and
grasshoppers also develop in this way.

A newly born baby has
a veiy large head, and
short arms and legs.

Southern
white admiral
{Limenitis
Camilla)

A two-year-old's legs
and arms have
grown a lot. Its legs
are now strong
enough for walking.

A caterpillar
has powerful
jaws but a
butterfly has
tubular

mouthparts and
can only drink
its food.

TAKING TO THE AIR
By changing shape, the same animal
can use diff erent kinds of food, and
move in different ways. A caterpillar
eats leaves, and spends all its time
on plants. But when it turns into a
butterfly, it feeds on nectar. It can
now fly far away to search for new
food plants, on which it will lay its
eggs if it is a female.

A megalopa
larva has well
developed
legs, no spine,
and a shorter
tail. It lives partly
on the seabed.

A mi rid bug (leaf bug) in the second, fifth, and
adult phases of incomplete metamorphosis.

A crab's zoea larva has a long
tail, and a curved spine on its
back. It beats its legs to keep
near the surface.

363

110W LIVING THINGS WORK

Genetics

Male and female sex
cells have a single
set of DNA molecules
each, which means
that they have half the
amount of a normal cell.

A fertilized cell has a
double set of DNA
molecules. In other
words, it has the
usual double set of
chromosomes.

Each DNA
molecule forms a
thread-like structure, or
chromosome. There are two copies
of each chromosome - one from
the father and one from the mother.

EVERY FORM OF LIFE, from an elephant to an alga, is
put together and controlled by a chemical “recipe”,
Instead of being written down, this recipe is in the form
of a chemical code. The code is contained in helical
(spiral-shaped) molecules of deoxyribonucleic acid
(DNA), which are packed away inside the cells of all
living things. The chemical code is very complex. The
code inside one human cell contains 50,000 to 100,000
separate instructions, called genes, and each one
controls a different characteristic. Genetics is the study
of the way that inherited characteristics are passed on.

r- — Bases linked
in pairs

The code
instructs the
cell to
assemble
proteins.

\ /

1 %

5 >

. t 1*

* 0

% • *. :
a*

*«

fi ii

* *
n

•5

* %

The DNA in a
chromosome is coiled up
on itself, and wrapped
around other chemicals.

The DNA molecule is in the shape of
a double helix, linked by chemicals
called bases, of which there are four
kinds. The sequence of these bases
makes up the cell's genetic code.

HUMAN CHROMOSOMES
This photograph shows all the 46
chromosomes in a single human
cell. They have been treated with a
special dye and arranged in pairs.

(The X and Y chromosomes are
on the lower right.) Every species
of plant and animal has a
characteristic chromosome
number. Some have
less than ten, others
over a thousand.

DNA is "unzipped"
while the code is
copied.

Chromosomes, genes, and dna

In a cell’s nucleus, there are several lengths of DNA. Each one is
called a chromosome. A gene is one area of a chromosome that
has the instructions to make one protein. DNA works by telling
a cell how to make the many different proteins that your cells
need to work. To do this, part of the DNA helix is temporarily
“unzipped”, so that its code can be copied. The copy moves out
of the nucleus. Once outside, it instructs the cell to assemble a
particular protein, which could be an enzyme, or collagen
(a protein in your skin), for example.

ROSALIND
FRANKLIN

The final break¬
through in the study
of DNA’s structure,
was made in 1953, by
British bio-physicist
Francis Crick (born
1916) and American
geneticist James
Watson (born 1928).
They suggested that DNA was a
double helix - a conclusion they
reached after studying X-ray
photographs taken by British X-ray
crystallographer Rosalind Franklin
(1920-58). She used X-rays to look
at DNA crystals. Crick, Watson, and
Maurice Wilkins (born 1916) got
the Nobel Prize for Physiology or
Medicine in 1962. Franklin died
before her contribution was
properly credited.

These flowers/
are chamomile
(Anthemis chia).

GENES AND PEOPLE
Unless you are an identical twin, you are
unique, because nobody else has exactly
your combination of genes. Genes
control all the inherited characteristics of
your body. Sometimes a single gene
controls a characteristic that we can see,
such as the colour of your eyes, but
usually several genes are involved. Many
of the characteristics you inherit are
modified by the way you live. For
example, your height depends on what
you eat, as well as on your genes.

Protein

being

assembled

NATURAL VARIATIONS
These flowers may look
the same, but each plant
has its own unique DNA,
because it was formed by
sexual reproduction. This gives
the plant a distinctive set of
characteristics. It might have
more flowers than others, or it
might put slightly more energy
into growing roots. Tiny variations
like this are important, because
they mean a species evolves (changes
with time). Some DNA variations are
more successful than others, so as one
generation succeeds another, their more
successf ul genes become more common.

MUTATIONS

DNA is an extremely long molecule, and it is frequently
damaged. Normally, this damage is automatically
repaired. But if the damage is extensive, it creates a
permanent new piece of genetic code, called a
mutation. Mutations normally have little effect if they
occur in body cells. But if they
occur in gametes (sex cells),
they can be passed on
from one generation to
another. Mutations
create new
characteristics in
living things.

Albino (white) colour is a
common type of mutation
in animals and plants. This
is an albino red squirrel.

364

HOW LIVING THINGS WORK

Meiosis

Meiosis is a special kind of cell
division that produces gametes (sex
cells). During meiosis, a cell divides
twice, so that it makes four new
cells. The new cells have only half the
amount of DNA in the original cell.
Each of their chromosomes has a new
and unique pattern, because the
original cell’s chromosomes swap
pieces just before division begins.
Unlike mitosis (ordinary cell division)
meiosis makes cells that have new
genetic instructions. A female gamete
is usually called an egg cell, and the
male gamete is a sperm cell.

The original male cell has a
double set of chromosomes.

The original female cell also has
a double set of chromosomes.

Qji

2 '

The male cell
divides by
meiosis. It
produces four
male sex cells, or
sperms. Each
one has a single
set of unique
chromosomes.

GREGOR MENDEL

Mendel (1822-84)
was an Austrian
H monk and botanist
who discovered how
characteristics are
inherited. He
patiently carried out
thousands of
experiments on pea
plants, cross-fertilizing
particular parents, and
studying the results. He found out
that inheritance does not work by
blending characteristics together, as
people then thought. Instead, they
are inherited in pairs. In each pair,
only one characteristic is usually
expressed (shown). Mendel worked
out the basic rules of genetics, but it
was not until the 20th century that
scientists rediscovered his work.

During fertilization, one male
gamete and one female gamete
join together. They make a
fertilized cell that has a double
set of chromosomes once more.

The fertilized cell has a
unique genetic blueprint. It
divides by mitosis to
produce a new organism.

All the DNA in a new
organism is a copy of the
DNA in the egg and sperm.

Only the
large cell can
be fertilized

Ginger cats are usually male (XY). The gene for
ginger is carried on the X chromosome, but it is
often masked if another X chromosome is
present, as it is in a female (XX).

HOW CHARACTERISTICS ARE INHERITED
Most cells contain two sets of chromosomes, one from
each parent. This means they have two sets of genes.
Normally one gene in every pair is dominant,
meaning that it masks (hides) the effects of its
recessive partner. Here, you can see how a pair
of genes controls the colour of pea flowers.

The dominant gene (labelled R) makes
flowers red. The recessive gene (labelled r)
makes the flowers white. However, its effects
are masked, unless there are two of them.

Each offspring plant
receives one flower
colour gene from each of
its parents. In the first
generation, there is only
one possible combination
of genes: Fir.

In the second
generation, there
are four possible
combinations of
genes: FIR, Rr,
rR, and rr.

One parent plant has two dominant
genes (RR), so its flowers are red.
The other parent has two recessive
genes (rr), so its flowers are white.

rr Recessive
genes usually
only show
their effects if
there are two
of them.

The female cell divides
by meiosis. It produces
four female sex cells,
or eggs. Each has a
single set of unique
chromosomes.

In animals,
the original
female cell
often divides
unequally. It
produces three small
cells (polar bodies), and
one large one.

HAPLOID AND DIPLOID
A cell with a full (double)
set of chromosomes is
called diploid. Most of the
cells in your body are
diploid. A sex cell only has
half the number of
chromosomes, so it is
called haploid. Sex cells
are haploid so that they
can join up with another
sex cell to make a diploid
cell. This cell can then
grow into a new organism.

Tortoiseshell cats are
always female, because
this colour can only be
produced by two
X chromosomes.
Only females have
the XX combination.

GENES AND SEX
In cats, humans, and
many other animals, two
differently shaped
chromosomes decide what sex an individual will
be. The chromosomes are known as X and Y. An
animal can either have two X chromosomes,
making it female, or it can have an X and Y
chromosome, making it male. It cannot have two
Y chromosomes, because it always receives one X
chromosome from its mother. As well as sex,
these chromosomes also determine some other
characteristics. In cats, they include fur colour,
while in humans, they include colour blindness.

The first generation offspring all have red
flowers. Although each has a recessive
gene for white flowers, its effects are
masked by the dominant gene.

One quarter of
the plants have
two recessive
genes (rr). Only
their flowers
are white.

Find out more

HOW EVOLUTION WORKS P.309
Cells p.338

Growth and development
p.362

Sexual reproduction p.367
Human reproduction p.368

365

HOW LIVING THINGS WORK

Asexual reproduction

An anemone gradually pulls
itself apart as the two halves
creep in different directions.

PRODUCTION LINE BIRTH
In spring and summer, female aphids
are of ten surrounded by dozens of
young. The females produce babies by
parthenogenesis (without mating),
and they multiply very rapidly. This
means that there are lots of aphids
when there is plenty of food. Later, as
the food supply starts to dwindle, their
young reproduce sexually.

CLONES

Sea anemones usually reproduce sexually
by releasing eggs into the water, but they
can also multiply by breaking off parts of
themselves, or by pulling themselves in
two. Some species concentrate on this
form of reproduction. They spread
over rocks, forming a group of identical
animals that share exactly the same genes.
Groups like this are called clones.

The two new animals are genetically
identical to their "parent", which is
the original anemone.

All LIVING THINGS REPRODUCE. Reproduction
and continuing the species is a basic feature of all
living things. But living things reproduce in two quite
different ways. Here, you can find out about one way.
It is called asexual reproduction, because it does not
involve sex. In asexual reproduction, there is just one
parent. Part of the parent buds off or splits away, and
this becomes a new individual. Asexual reproduction
is simple and quick, but it does have one result
which can be a drawback under certain
conditions. The parent and young share
the same genetic material, so they have
exactly the same characteristics. If
the parent has a disadvantage, such
as low resistance to a disease, its
offspring will have it too.

Asexual reproduction

IN ANIMALS

Asexual reproduction is widespread
in plants, but it is less common in
animals. The first person to see
an animal reproduce in this
way was Antoni van
Leeuwenhoek, one of
the earliest users of the
microscope. In 1701, he was
watching a tiny animal called a hydra,
which lives in ponds. He saw how parts
of it bud off to become new animals.

A young hydra polyp
attached to its parent. The
new polyp eventually
breaks away to live by
itself. This hydra is
Hydra vulgaris.

BUDDING YEAST
Yeasts are microscopic single-
celled fungi. They reproduce
asexually by budding off parts
of their cells. A yeast cell can
bud every two hours. The new
cells sometimes start to bud
before they have completely
separated from their parent, so
a branching chain is produced.

Parent

strawberry

plant

SPREADING BY RUNNERS
Many plants reproduce in two
different ways at the same time.
Strawberries have flowers, which
make seeds by sexual reproduction.
They also send out horizontal stems,
called runners, which form new
plants by asexual reproduction. Each
runner develops several young plants,
and these gradually take root. If a
strawberry patch is left untended,
new strawberry plants soon cover
the ground.

NEW BULBS

Bulbs contain food, which is stored
in special leaves that are packed
tightly together. As a
bulb grows, it forms
new small bulbs
called bulbils
around its base.

Daffodil
bulb with
bulbil

PROPAGATING CROPS
Bananas are never grown from
seed. Instead, a farmer simply cuts
off new shoots, and plants them.
With crops like this, the plants will
all have the same characteristics. If
one catches a disease, the rest may
do so as well. This lack of variety is
a major problem of asexual
reproduction.

Find out more

Single-celled

ORGANISMS. P.314

Growt h and

>EVELOPMENT P.36^
Fact finder p.422

)

366

ITOW LIVING THINGS WORK

Sexual reproduction

COURTSHIP AND MATING
Before grebes mate, they carry out
a series of complicated dances.
This kind of behaviour, called
courtship, is common in many
animals. It helps both partners to
get used to each other, and
ensures that they choose a suitable
and healthy mate. Courtship is
then followed by mating.

Californian mountain
kingsnakes (Lampropeltis
zonata) mating

(Podiceps
cristatus)

There ARE ALWAYS TWO PARENTS in sexual reproduction.
Each parent makes gametes (sex cells) by a special kind of cell
division called meiosis. The male gamete (the sperm) and the
female gamete (the egg) are brought together, and a new cell is
formed. This is fertilization. From this fertilized cell, a whole new
organism develops. Sexual reproduction is more complicated than
asexual reproduction, but it has an important advantage. Instead of
being the same as one of their parents, sexually produced offspring
are unique. They have a unique combination of genes, so that they
Great crested grebes have a completely new mixture of characteristics. This

means that some of them may be better
equipped in the struggle to survive.

EXTERNAL FERTILIZATION
In some animals, the eggs and
sperm join together outside the
female’s body, but the animals
still have to come together.
The male stickleback
(Gasterosteus aculeatus)
makes a nest, in which the
female lays her eggs. The
male then adds his sperm to
the eggs. Most animals with
external fertilization have to
produce lots of eggs so that
enough will be fertilized.

Sporophyte stage

Spores
produced
X - by meiosis

A new
sporophyte
starts to
grow.

Fertilization

Internal

FERTILIZATION

For sexual reproduction to work, the male and female sex
cells have to be brought together. In some animals, this
happens through mating. Snakes and many other land
animals have internal fertilization: when two snakes mate,
the male injects his sperm into the female so that
fertilization of her eggs takes place inside her body.
Animals that have internal fertilization produce fewer
eggs and sperms, as these are more likely to come together.

SEX CELLS

Sex cells (gametes) have exactly half
the amount of genetic material of
ordinary cells. They are specially
shaped so that they can join
together. In some plants and
animals, the sex cells are the same
size. But more often, the female sex
cell is much larger than the male.
Female sex cells (eggs) stay in one
place, while male sex cells (sperms)
swim towards them.

The sea lettuce (Ulva lactuca) has
identical male and female sex cells.

Flowering plants have several
female sex cells in an embryo sac.
The male cells are contained in
pollen grains.

In most animals, the egg is far
bigger than the sperm.

Female

gametophyte stage
produces eggs.

Male
gameto¬
phyte
stage
produces
sperms.

In ‘‘thrum’’ primrose flowers
the stamens (which produce
the pollen) are high up, and
the stigma is short

“Pin” primrose flowers
have a long stigma (the
female part). The
stamens are low down.

ALTERNATING GENERATIONS
In some plan t lif e cycles there are two
different forms of the plant. In the brown
algae Laminaria , the “adult” form (called
the sporophyte) produces spores by
meiosis. These develop into male and
female plants called gametophytes. It is
this stage that produces the gametes (sex
cells). The eggs and sperm come together
in the water to produce a fertilized cell.
This grows into a sporophyte, and the
cycle starts again.

ENSURING CROSS-FERTILIZATION
Many plants have both male and female parts in
their flowers. They can often fertilize themselves, but
they usually have features that encourage cross¬
fertilization (fertilization with sex cells from another
plant). Gross-fertilization is useful, because it makes
a plant’s offspring more varied. Primroses (Primula
vulgaris) have two types of flowers, but only one type
is found on a plant. Each flower type can only
fertilize the other, so cross-pollination is guaranteed.

Find out more

Plants without flowers p.316
Flowering plants p.318
Fish p.326
Reptiles p.33§

Birds p.332
Cells p.338
Gene pics p.364
Human reproduction p.368
Fact finder p.422

367

HOW LIVING THINGS WORK

Human reproduction

Like every person on earth, you started life

as a tiny fertilized cell. This cell was formed when
one of your father’s sperms (sex cells) joined up wit!
an egg cell in a tube that leads into your mother’s
^ womb (uterus) called the fallopian tube. Almost
immediately, the fertilized cell began to change. It
started to divide, and it then settled on the lining of
the womb. Nourished by your mother’s blood, it
divided again and again, and slowly your
body began to take shape. After nine
months in the warmth and ’ m

\ darkness of your mother’s
body, you were Prostate

rporl^; In Kp Knrn gland v

From the start of
puberty, sex
hormones
produce changes
in the male body.
The sex organs
become fully
developed, and
facial hair starts
to grow.

When a woman
has a baby, her
breasts make
milk to feed it.

The ovaries
store egg
cells. They
also release
hormones
which control
a woman's
reproductive
cycle.

Scrotal sac

A woman is born
with all her egg
cells, but a man
makes new
sperm cells all
the time.

Bladder

Sex hormones
circulate in the
blood, and
make a woman's
body ready to
look after a
developing child.

\ / | MALE SEX ORGANS
I I ( I Male sex cells, or
X J J \ sperms, are made in

two glands called
,s testes. During

lovemaking, the sperms are mixed
with liquid from the prostate
gland that makes the sperms swim.
This means they can reach the egg
in the woman’s uterus.

FEMALE SEX ORGANS
A woman’s egg cells are stored
inside two glands called ovaries.
From the age of about 13, one
egg cell is released every 28 days.

The egg is now a hollow
ball of cells. It lands on
the lining of the uterus
and gradually develops
into an embryo, then a
foetus. ,

Penis

The fertilized egg
starts to divide rapidly
by mitosis.

The egg is fertilized by
a sperm swimming
up the fallopian
tube -

Lining of the
mother's uterus

Mother's cells which
have been digested
to provide nutrients

/ * I The egg is

'SJ collected by a

_ f funnel, and is

£ carried along the

f fallopian tube.

The empty follicle
produces a hormone that
prepares the lining of the
womb to receive the egg.

These cells will
develop into the
placenta and the
umbilical cord.

Every 28
days or so, a*
ripe egg cell is released
from a bubble on the
ovary called a follicle.

The ovaries take
turns to produce one
egg each month.

The lining of the uterus builds
up each month to receive the
egg. If the egg has not been
fertilized, the lining of the
uterus breaks down. This is
menstruation.

These cells will
develop into
the baby.

The uterus

The uterus is the

which feeds

This fluid-filled
cavity will develop
into the amniotic fluid,
the "water” that the
baby floats in.

organ

and shelters a foetus (developing baby).
The inside lining develops to feed a
fertilized egg, then the embryo, and later
the foetus. The uterus itself is very
muscular - it has the strongest muscles in
the human body. These push the baby out
during labour, with help from the mother’s
other muscles in her abdomen and chest.

Sperms swim into the uterus \

through a tiny gap in the cervix.

The vagina holds the penis during
lovemaking so that the sperms are
ejaculated (pumped out) as near the
egg as possible. The vagina is also the
canal through which the baby is born.

IMPLANTATION
When a fertilized egg lands on the
wall of the uterus, it starts to break
down some of the mother’s cells. To
begin with, it is nourished by these
cells. Later, it gets oxygen and
nutrients from its mother’s blood
through a spongy organ called the
placenta. This is connected to the
foetus by a long cord called the
umbilical cord. These two organs
take the foetus’s waste products back
to the mother. The placenta also
produces hormones in pregnancy.

Breasts
produce milk
very soon
after birth.

CHANGES IN PREGNANCY
To begin with, the foetus
(developing baby) takes up
little room, but by the ninth
month it fills the whole of the
uterus and this pushes up
against the mother’s
stomach and diaphragm.

The mother’s body adapts
to these changes. Her heart
pumps more blood to
nourish her growing child.
She eats much more to feed
it, and her breasts grow in
preparation for breast¬
feeding after it is born. She
also prepares herself
mentally for the new baby.

The foetus
usually lies
upside
down, with
arms and
legs tucked
close to its
-- body.

BREAST & '■M/mtmm

FEEDING

Most baby |

mammals \

are fed with . ^
milk from "

their mother’s breasts. Milk
contains a perfectly balanced
mixture of nutrients designed for
the baby, and it is easily digested.
Milk also has the advantage of
being readily available.

Find out more

Mammals p.334
Primates p.336
Growth and development
p.362

Genetics p.364
Sexual reproduction p.367

•The
umbilical
cord
carries
blood from
the foetus to
the placenta.

368

ECOLOGY

The weather is part of the
rabbit’s environment. The
rabbit has to survive in
different conditions. It
needs clean air to breathe
and water to drink.

Animals that live
in the rabbit’s fur,
such as fleas, or
organisms

Animals that eat
rabbits, such as foxes

The STUDY OF LIVING THINGS in their natural
surroundings is called ecology. And their surroundings
are called their environment. Ecology is about seeing
the whole picture as well as the pieces. By studying an
animal’s environment, ecologists can begin to
understand why the animal behaves in a
particular way. But ecology is still a “new”
science, and the natural world is very
complex. Ecologists know that problems exist
but are not always sure how serious they are or

how to solve them.

Rabbit’s environment

The conditions in which an animal lives, and the other
species of animals and plants that live in its area, all
affect the animal’s own life. This is why, when ecologists
study the environment of an animal such as a rabbit,
they study everything living and non-living that is
connected with it. This includes animals that hunt it,
its food, other rabbits, the weather, air, and soil.

Plants that the rabbit
eats such as grass,
dandelions, and clover

Soil in which the rabbit digs
burrows for shelter from the
weather and predators, and
to protect its young

HUMAN ENVIRONMENT
Unlike most other animals,
humans can change their
environment to suit their way
of life. This does not always
help plants and other animals.
Human ecology is the study of
how humans change the
environment and how these
changes affect humans themselves.

GATHERING FACTS AND FIGURES
The information that ecologists
need to collect involves a lot of
t counting, weighing, and measuring
- on land and under water.
Sometimes figures are fed into
computers that work out the
possible effects of certain changes
to an area. Ecologists can then advise
people how to treat the environment.

Other
animals, such as
squirrels and mice, that
eat the same food as
the rabbit

Other
rabbits that
live together in
the same warren (several
burrows). Rabbits breed together
to produce more rabbits and help
each other to survive.

ERNST HAECKEL

German biologist Ernst Haeckel
(1834-1919) was, in 1869, the
first to use the word ecology.
He defined it as “the study
of the economy, of the
household, of animal
organisms”. He took the word
from the Greek oikos, meaning
“house” or “place to live in”.
Haeckel supported Darwin’s
theory of evolution by natural
selection. His idea of ecology was
forgotten until about 1900 when
biologists began to study it seriously.

Animals
that live in
the same place, such
as worms in the soil

369

ECOLOGY

The biosphere

The earth is a complicated system. The part
in which life exists is called the biosphere. Zfowis
an Ancient Greek word meaning “life”. The
biosphere extends a little way above and below the
surface of the planet. The habitat is made up of
distinct areas, each with its own characteristic
climate, soils, and living communities of plants
and animals. These areas are called ecosystems.
Each one consists of a number of parts which are
related in such a way as to keep the whole system
going. Although distinct, each ecosystem is not
closed. Sunlight and rain enter it, water drains
from it, nutrients enter and leave through the
soil, and plant seeds and animals come and go.

LARGE AND SMALL
An ecosystem can be as small as
a drop of rainwater on a leaf, or
as large as an ocean. Both have
different characteristics from
the surrounding area, and
both contain groups of living
things, which interact with
each other. A single tree and
a huge forest arc also
ecosystems. Human skin can
even be studied as an ecosystem
as colonies of bacteria and
mites live here.

Units within the biosphere

To make the biosphere easier to study,
ecologists break it down into smaller
units. Information about each unit
can then be fitted together to give
a more complete picture. One
ecosystem can be studied as a
whole, or the living things
within it can be studied
individually.

NICHE

A niche is the position
of a living thing within
an ecosystem,
including where it
lives, what it absorbs or
eats, how it behaves,
and how it is related to
other living things.

The niche has been
called the “profession”
of a species.

HABITAT

A habitat is the natural
home of a group of plants
and animals. This group of
living things is called a
community. The habitat is
sometimes called the
“address” of a species. It
contains several niches. Trees
are an example of a habitat.

BIOSPHERE
The biosphere
covers the whole
surface of the Earth.

It is the living part of the
planet, and includes the
atmosphere. It contains many
different ecosystems.

THE EARTH

The Earth is the only planet that we
know for certain contains life. It has both
water and an oxygen-rich atmosphere,
which protects the planet from the Sun’s
more harmful rays. In 1996 scientists found
signs indicating that Mars may once have had
living things. Astronomers think that other stars
may have planets similar to Earth.

ECOSYSTEM

An ecosystem is a distinct area in the
biosphere which contains living things.
It includes the rocks and soil underneath
the ground, the surface of the ground, and
the air above it. It contains several habitats.

A forest is an example of an ecosystem. The
largest ecosystems, such as rainforests and
deserts, are called biomes.

JAMES E. LOVELOCK

British scientist James
Lovelock (born 1919)
put forward his “Gaia
hypothesis” in the
1970s. Gaia is an old
Greek term for “Mother
Earth”, or “Earth
goddess”. After studying the
atmosphere on Mars, Lovelock
began to study Earth’s atmosphere.
He suggested that the atmosphere is
regulated by the biosphere. All living
things on Earth can be thought of as
part of one being that can change its
environment to suit its needs. Gaia
will ensure conditions are right for
its own survival, even if humans
make the Earth unfit for themselves.

370

ECOLOGY

The world’s ecos\stems

Ecosystems are distributed over the Earth
mainly according to climate. There are
zones of different climates ranging from
cold and dry at the Poles, to hot and wet
at the Equator. Plants and animals are
adapted to the conditions and are
associated with each other to form
communities. They have particular roles
within each ecosystem, competing for
the resources to survive.

Temperate forests contain
conifers and broadleaved trees.
They are in regions that are not
very hot or cold, and have regular
rainfall most of the year.

Deserts are mostly hot, with
hardly any rain. They are found
in North and South America,
Asia, Africa, and Australia.

Polar and tundra lands are at the far
north and south of the Earth, in the Arctic
and Antarctic. It is freezing cold all year
round in the Polar lands. These merge into
tundra lands farther away from the Poles.

Seashores are half land and
half sea. They form a constantly
changing ecosystem found
around the edges of all continents.

Grasslands are huge areas of
land where chiefly grasses grow.
They are found mainly in Asia,

North and South America, and Africa.

Oceans make up the
largest ecosystem of all.
They are all linked together.

Wetlands include marshes,
swamps, and bogs, both
freshwater and saltwater.
They are found on all
continents except Antarctica.

Tropical rainforests grow in Central
and South America, central Africa,
Southeast Asia, and northern Australia.
They are mostly near the Equator, so
are hot and wet most of the year.

Towns and cities replace
the original ecosystems, and
form a new ecosystem for
wildlife to adapt to. They are
warmer and less windy than the
surrounding countryside.

Mountains are
found on all the
continents. They
include most of the
major ecosystems
because climatic
conditions change at
different heights.

Rivers and lakes are
freshwater ecosystems.
They are found over most
of the world’s land surface.

ECOSYSTEM BOUNDARIES

SUCCESSION

Communities develop until
they reach a stable form
known as the climax
community. The process of
change, for example from
grassland to woodland, is
called succession. This
example is primary
succession. Secondary
succession is when an
ecosystem is destroyed by
nature or by people, and
then, after a time, recovers.

Grazing
animals keep
grassland as it
is, by eating
tree seedlings.

If the number of
animals decreases,
trees may start to
grow and stop
sunlight reaching
the grass.

Eventually, the
trees take over
the area and
form woodland.

Each ecosystem is different from
its surroundings in some way. Its
surroundings arc parts of other
ecosystems. Some ecosystems have
distinct boundaries, such as
between a forest and a lake. The
habitats and niches suddenly
change. But many ecosystems
merge together. The area where
they merge is called an ecotone. It
contains animals and plants from
both ecosystems.

Find out more

Cijmatks p.244
Atmosphere p.248
Earth p.287

Cycles in the biosphere p.372

371

ECOLOGY

Cycles in the biosphere

eat
and
some
carbon.

LEAD POISONING

Fumes from traffic
are responsible for
releasing more than
225,000 tonnes of
lead into the
atmosphere every
year. The lead is
mixed into the air
and absorbed by
humans and other
animals, poisoning
their bodies.

Children are
especially at risk.

Night Day

Oxygen cycle

Living things take in oxygen from the air. They use it to
release energy from the food they eat. They may also use it,
together with carbon, hydrogen, and nitrogen, to build new
molecules in their bodies. Oxygen is released back into the
atmosphere by green plants during photosynthesis, and by
plants and animals as part of carbon dioxide.

Part OF YOU might once have
been part of a dinosaur. This is
because the basic substances in your
body have been recycled and used by
other animals, and plants, before you
used them. Living things take in
water, carbon, nitrogen, and oxygen
and use them to live and grow. If
these resources were used only once,
they would run out. All animals and
plants respire (breathe), grow, and
eventually die and decompose.
Decomposition releases the
substances in their bodies back into
the biosphere to be used again.

Decomposers,
worms, bacteria,
give out carbon dioxide
they feed and respire.

Plants and
animals die
and their
bodies decay.

Carbon cycle

The bodies of all living things are based on the element
carbon. The carbon comes originally from carbon dioxide gas
in the atmosphere. Green plants and some bacteria take this
in, and use it to make food. When animals eat the plants, they
take in some of the carbon. Carbon dioxide goes back into
the atmosphere when living things breathe out, or when they
produce waste, die, or decay.

Oxygen in the atmosphere

take in oxygen and
give out carbon
dioxide at night.

Plants take in
carbon dioxide and
give out oxygen
during

photosynthesis in
the daytime.

Animals breathe in
oxygen % and breathe
out carbon dioxide.

Carbon dioxide in the
atmosphere

Animals
breathe out
carbon
dioxide.

Animal
dung
contains
- carbon.

GLOBAL WARMING

When we burn oil, coal, and wood, we release carbon
dioxide into the atmosphere. All this extra carbon
dioxide is creating a “blanket” around the Earth. Most
of the short-wave radiation from the Sun can get
through the blanket. But most of the long-wave
radiation from Earth cannot escape,
causing the Earth to
get hotter and hotter.
This is called the
“greenhouse effect”
and causes global
warming.

Long-wave radiation
bounces back and forth
between the surface
of the Earth and the
blanket.

Green plants give out
carbon dioxide during
respiration.

Green plants take
in carbon dioxide
during

photosynthesis

372

ECOLOGY

EUTROPHICATION

Farmers add nitrates to the
soil, as fertilizers, to make
better crop yields. These can
get washed into waterways.
Then too many plants and
animals grow in the water,
affecting the ecosystem there.
This is called eutrophication.

POLLUTION

Factory waste has
polluted many
rivers and lakes,
killing the wildlife.
And oil spilt at sea
is very dangerous to
wildlife. It clogs
animals’ feathers
and fur, gets inside
them, and stops
them finding food.
They then die of
cold and hunger.

Nitrogen cycle

All living things need nitrogen to make proteins.
But most cannot make use of nitrogen gas in the
air directly. The nitrogen has to be fixed, or
combined with other elements, to form
compounds called nitrites and nitrates.

Plants can take in nitrates and animals
get their nitrogen by eating the
plants. This fixing process is carried
out by special nitrifying bacteria,
algae, and lichens. The bacteria
live in the soil or on the roots
of plants such as peas, beans,
and clover. Denitrifying
bacteria break down
animal waste and dead
plants and animals, to
release nitrogen back
into the atmosphere.

Nitrogen gas in
the atmosphere

Nitrifying bacteria in plant roots
convert nitrogen compounds in the soil
to nitrates.

Water cycle

Water on the Earth’s
surface, such as seas and rivers, is
heated by the Sun and evaporates as
water vapour into the atmosphere. As it rises
up into the air, it cools and condenses back into
water again. Water droplets collect together to form
clouds and then fall back to the surface as rain.

ACID RAIN

Poisonous gases from power
stations and vehicles mix with
water in the air. This then falls as
acid rain and becomes part of the
water cycle. Acid in the rain can
damage wildlife in all ecosystems
where it falls. It also affects stone,
causing statues and buildings to
crumble away. Gases can be carried
long distances by the wind, so
pollution produced in one country
can fall as acid rain in another.

Lightning makes
nitrogen and
oxygen combine
and fall in the
rain as weak

Animals eat plants
containing nitrates.

Water vapour
cools to form
clouds.

Water falls
back to Earth
as rain.

Water flows
back into
the rivers
and seas.

Water
evaporates
from the
Earth’s surface.

Poisonous

fumes are

released

into the

atmosphere.

Acid rain
damages
plants, animals,
and buildings, and is
mixed into rivers, lakes,
and seas.

Denitrifying bacteria take in
nitrates and release nitrogen
back into the atmosphere.

The gases mix with
water in the ait

Animal waste and dead plants
and animals decay and release
nitrogen compounds into the soil.

Nitrates in the soil

Plant roots take up
nitrates from the soil.

Poisoned
water falls as
acid rain.

Nitrifying bacteria in the soil
convert nitrogen compounds to nitrites.

Nitrifying bacteria in the
soil convert nitrites to nitrates.

— Find out more -

Carbon p.40
Nitrogen p.42
Oxygen p.44

Changing climates p.246
Formation of clouds p.262
Rain p.264

Photosynthesis p.340
Transport in plants p.341
Cellular respiration p.346

373

ECOLOGY

People and planet

The EARTH IS ABOUT 4,600 MILLION YEARS OLD. If this
time was fitted into one day, humans would have been around
for less than a second. The United Nations estimates that world
population (5,700 million in mid-1995) will be nearly 8,000
million by the year 2015. People need food and water, space in
which to live, air to breathe, and energy to drive their machines.
This leaves less and less space and food for other animals and
plants. Many environmental problems have been caused by
people. Global warming, acid rain, and holes in the ozone layer
are three examples. There are no simple solutions to these
problems. But we are becoming more
aware of what harm we are doing.

DANGEROUS CHEMICALS
Some of the chemicals we spray on crops are
poisonous to people as well as to the environment.
Protective clothing should be worn but it is not
always available in developing countries.

Energy resources
such as coal

Give and take

People take many resources
from the planet, but put back mainly
harmful things, such as waste and pollution.
Coal, gas, oil, and metals will run out. We
need to find some renewable resources
before the non-renewable ones are all gone.

We put
back:

Waste
from homes,

farms, and on cro P s place of the ones

factories cut down are a good

thing to put back.

Nutrients from the Water for drinking,
soil to grow crops washing, irrigating
fields, and for use in
factory processes

We take
out:

Poisonous
fumes from
power stations,
factories, and vehicles

Wood
houses,
furniture,
and paper

Stone and clay for
building, and minerals
for factory processes

POPULATION EXPLOSION
It took thousands of'years, until the
1830s, for the number of people in
the world to reach 1,000 million. But
it took only 100 more years for there
to be more than 2,000 million. The
world population has doubled in the
last 40 years, but the rate of increase
has slowed down, and the United
Nations estimated in 1995 that world
population would stabilize at 11,600
million by 2050. This picture shows
houses huddled together on a
hillside in Rio de Janeiro, Brazil.

POLLUTION DISASTERS

1953-60 Mercury poisoning in shellfish
in Minimata Bay, Japan, causes brain
damage to people.

1976 Herbicide leak in Seveso, Italy,
poisons hundreds of people. Domestic
animals in the area have to be killed.

1984 Leak of chemicals from factory
in Bhopal, India, kills 2,500 people.

1986 Nuclear reactor accident at
Chernobyl, Russia, af fects a wide area
with radioactive poisoning.

1989 Tanker spills 40,000 tonnes of oil
off the coast of Alaska which kills
thousands of animals.

1993 Tanker spills 84,000 tonnes of
oil into the sea off Shetland Islands,
Scotland, polluting farms and beaches,
and killing wildlif e.

374

ECOLOGY

CFCs produced by factories
drift up into the atmosphere
and destroy the ozone.

A complete ozone
layer stops most of
the Sun’s ultraviolet
radiation getting
through to Earth.

Too much ultraviolet
radiation gets through
holes in the ozone,
harming all life below.

An ozone molecule consists of three
oxygen atoms. When CFCs reach the
ozone layer, the higher levels of
ultraviolet radiation break up the
CFCs and release chlorine atoms.
These join up with one of the oxygen
atoms from each ozone molecule, so
destroying the ozone molecules.

Hole in
ozone

Ozone layer

About 15-50 km (9-30 miles) above the Earth is a layer of ozone.
This ozone layer shields the Earth from most of the Sun’s
harmful ultraviolet radiation. Too much ultraviolet can change
the genetic structure of plants and animals and cause skin
cancer in people. Holes have formed in the ozone layer,
allowing more of the ultraviolet rays through to the Earth. In
the Antarctic, high levels of ultraviolet are stopping plankton
from photosynthesizing (making food using sunlight) which
disrupts the food chains in the sea.

HOLE OVER ANTARCTICA
In the 1980s, scientists discovered a hole in
the ozone layer over Antarctica, as big as
the United States. This special
photograph, taken f rom space, shows
the hole clearly. A smaller hole has also
been found over the Arctic and the
ozone layer is becoming thinner over
other parts of the planet too.
Scientists blame mainly gases called
chlorofluorocarbons (CFCs) for the
destruction of the ozone. CFCs are
used in some refrigerators, aerosols, air
conditioners, f ire extinguishers, and in
the production of some kinds of polystyrene
and cleaning substances.

Living pollution clues

By studying living things, we can tell how polluted the air
or water is. Some living things can stand a lot of pollution
while others thrive only where the air is clean. Lichens are
very sensitive to air pollution because they absorb
minerals from rainwater all over their surface.

Poisons in the rain soon build up in their tissues
and kill them.

Leafy lichens such
Bushy Usnea as Parmelia species

lichens grow can stand a small

only in clean air. amount of pollution.

Crusty lichens such as
Xanthoria species
mean the air is quite
badly polluted.

Only a bright green, powdery
alga called Pleurococcus,
can grow in very polluted air.
There are no lichens.

Stone-fly nymphs such
as Perla bipunctata live
only in clean water.

Flat-tailed maggots, the
larvae of hoverflies
(Eristalis species),
breathe oxygen
ttr directly from the
air through a long
tube so they can live
in very polluted water.

Find out more

Freshwater shrimps,
such as Gammarus
species, can put up with a
small amount of pollution.

Bloodworms, which
are really midge
larvae of Chironomus
species, can stand
bad pollution.

Catalysts p.56
Energy' sources p. 134
Atmosphere p.248
Photosynthesis p.340
Cycles in the biosphere p.372
Wastes and recycling p.376
Factfinder p.424

375

ECOLOGY

WASTES and RECYCLING

In THE NATURAL WORLD, nothing is wasted. Living things called
decomposers eat dead and decaying material. The decomposers
break everything down so it can be recycled and used again. The
material is said to be biodegradable. But this natural recycling is
upset by the huge amounts of wastes produced by people. Most of
this, such as tin, glass, and most plastic, is not biodegradable. When
we throw it away, it stays for hundreds of years. Even if it rusts or
breaks into tiny little pieces, it cannot be eaten by the decomposers.
It pollutes the atmosphere, the land, and the water. We can recycle
material by sending it back to be used again instead of throwing it
away. And we can try to avoid using non-biodegradable material and
buy only items with biodegradable, or very little, packaging.

DECOMPOSERS

When an animal dies, it is recycled by nature.

The larvae of the flies - maggots - will be the
decomposers on this dead shrew. Decomposers
help to clean up the environment and make
material available for other plants and animals to
use. When material has been broken down into
small enough pieces, bacteria and fungi, the
most important decomposers, can work on it.

Rubbish dumps

Human rubbish has to be put somewhere.
Most methods of disposing, or getting rid
of it, could harm the environment. A lot of
our rubbish is dumped into holes in the
ground, called landfill sites. Heavy vehicles
spread it out and squash it so it takes up less
space. Soil is put on top of the rubbish each day
to stop birds and animals feeding there, and
spreading disease. Although this hides the rubbish,
poisonous liquids can leak out, the rubbish can get hot
and catch fire, and gases are produced which can explode.

AVERAGE RUBBISH

In highly industrialized countries, where most
people have a modern way of life, an average
family throws away over 1 tonne of rubbish
every year. Most of their rubbish consists of
paper from packaging and kitchen waste. A
lot of this could be recycled and used again.

Paper and cardboard 30%

Kitchen waste 23%

Rubbish in an average
family’s dustbin

Glass 10%

Metals 9%

Plastics 5%

Cloth 3%

Dust 10%

rubbish 10%

Keep the heat in by
covering the heap
with a piece of old
carpet or sacking.

BUILDING
A COMPOST HEAP
Dead leaves and other
plant material are broken
down in the soil into nutrients
f or plants to use. You could give
plants in your garden extra nutrients
by mixing compost into the soil. Instead of
throwing away all your vegetable peelings,
dead flowers, and leaves from the garden,
make a compost heap. Collect layers of
plant waste in a large container outside.
Cover each layer with soil to keep in the
heat caused by decomposers eating the
dead plants. Keep the compost heap damp
because decomposers like warm, wet
conditions. It will take several months for
the compost to form. Be careful as the heap
can get very hot inside, and even catch lire.

Find out more

Bacteria p.31 3
Fungi p.315
Nutrition p.342
Cycles in tiie biosphere p.372
People and pianet p.374
Conservation p.400

376

ECOLOGY

FOOD CHAINS and WEBS

Bears

Beavers

FOOD CHAIN

A food chain is a series of living things linked together because
each one is food for the next, for example, plant to rabbit to fox.
Most food chains have only three or four links. By the fourth link,
all the energy has been used up.

The LIVING THINGS in a community are linked through their
food. For example, a fox, a rabbit, and a plant are linked
because the rabbit eats the plant and the fox then eats
the rabbit. These links are called food chains.

Animals and plants get the energy they need from
their food. Plants use the Sun’s energy to make
their own food. They are called producers.
Animals cannot make their own food, so they
have to eat plants or other animals. They are
called consumers. Animals often eat more
than one kind of food so they are part of a
number of food chains. Several food chains
can be joined together into a food web.

The steps get
smaller as
there is less
energy at the
top of the
pyramid than
at the bottom.

The small
amount of
poison on
each seed
builds up
into a larger
amount of
poison in the
body of birds that
eat the seeds.

Trophic level 4 has
fewer living things
because there is
less energy
than on the
levels below.

Poison from
several birds
collects in one
bird of prey.

POISON IN A FOOD CHAIN
Poisons build up as they are passed
along a food chain. Chemicals
sprayed on to a field of crops to kill
insects are taken in by birds that eat
seeds from the crops. If a bird of
prey eats several of the smaller
birds, it takes in a large amount of
poison. This may be enough to kill
it or cause it to lay eggs with thin
shells. These break when the
parent bird sits on them in the nest.
The build-up of poisons is called
bioamplification.

j£ Insect
larvae

Animal

plankton

Freshwater

shrimps

Plant plankton

Food web

A food web can include living things from several ecosystems.
In this food web in a lake community, some animals and
plants live in the water, and some live on land. The producers
are water plants and plant plankton. These are eaten by
herbivores (plant eaters), such as animal plankton, snails,
insects, and some fish. The herbivores are eaten by
carnivores (meat eaters), such as other insects, fish, and
mammals. A change in the number of a species at one
link will affect the plants and animals in the whole web.

JONATHON
PORRITT

British lecturer and
writer, Jonathon Porritt
(born 1950) is one of
the leading activists
in educating people
about the importance
of looking after the
Earth and its wildlife. He
became involved in“green
politics”, stood as a candidate for the
British Green Party, and became
Director of Friends of the Earth. In
1990, he stood down from his
position in order to concentrate on
lecturing, broadcasting, and writing
on green issues around the world.

Trophic
level 3

Trophic
level 2

Trophic
level 1

A pyramid of energy

TROPHIC LEVELS

One way of studying a community is to group the living
things into feeding levels called tfophic levels. Trophe is a
Greek word meaning nourishment. Trophic levels are
based on the numbers or mass (biomass) of living things
at the same stage in a food web, or on the amount of
energy stored by a group of living things at one stage.
They are drawn as steps, usually forming a pyramid,
because the amount of energy in living things decreases
as it is transferred to each successive level.

Find out more

Photosynthesis p.340
Nutrition p.342
Feeding p.343
Digestion p.345
The biosphere p.370
Wildlife in danger p.398

377

ECOLOGY

Animal groups

A PACK OF WOLVES, a herd of deer, a school of fish, and a
flock of birds are all examples of animal groups. Animals may live
in groups all the time or just come together to nest or feed in a
particular area at a certain time of year. Members of a group are
often related to each other. They may share out the jobs, such as
collecting food, caring for the young, and defending the
group. Living as a group allows the young animals to
learn skills and behaviour from the High-ranking ■

adults. In this way they are more likely wolve$ mark ,he ^

' ' . ' edges of their

to survive and can pass on their territory with their

knowledge to the next generation. S wXesfrom" S

other packs / \

to keep out.

Wolves hunt i n groups. This
allows them to catch large
animals such as moose.

Wolves howl to
warn rival
packs to keep
away from
their territory.

Young cubs learn
by watching the
adults and
^ copying what
they do.

High-

ranking

wolves hold *' %
their tail up in
the air and prick i gy
their ears up.

Low-ranking wolves hold,
their tail low to show they
are submissive.

Wolf pack

The members of a pack of wolves
(Canis lupus) help each other to survive b)
hunting together and defending the cubs.
Within a pack, each wolf knows its own
place. The high-ranking wolves tell the
others that they are dominant, or
superior, with special positions of the
body, called body language. The low-
ranking wolves also use body language
to show that they are submissive - they

A submissive wolf lies on its
back to show the dominant
wolf it will not fight.

The straight line part of the dance represents
the angle between the Sun and the food.

JANE GOOD ALL

English scientistJane Goodall
(born 1934) began to study
chimpanzees at the Gombe m-'

Stream Game Reserve in 6^

Tanzania, Africa. After years of
research, following chimp
groups through the forest,

Goodall began to piece together

details of their family life. She

could then work out the best way

to protect the chimps. The Jane I j

Goodall Institute focuses attention

on the plight of chimpanzees. They are” i!

an endangered species due to destruction of

their habitat, hunting, and illegal trade.

BIRD COLONIES
Many seabirds, such as gannefs
(Sula bassana), nest in large groups
called colonies. They sit just out of
pecking distance of each oiher.
Nesting in numbers is safer as
enemies are less likely to attack and
birds warn each other of danger.

BEE DANCE

Honeybees (Apis mellifera) run in a
figure-of-eight pattern to tell other
bees in the hive where to find a
good supply of food. The speed of
the “dance” tells the other bees
how far away the food is. The faster
the dance, the nearer the food.

Find out more

WlL

Birds p.332
Primates p.336
Feeding p.343

DUFF. IN DANGER P

Fact finder p .424

.398

378

ECOLOGY

Partnerships

DIFFERENT SPECIES OF PLANTS and animals can live together. In some
cases, the partnership helps both species. This is called mutualism. In other
cases, one of the partners is worse off. For example, a flea living on a dog
does not help the dog. The dog is bitten and gets itchy skin. The flea is
described as a parasite. In some partnerships, one of the species gains and
the other is neutral - neither gaining nor losing. A partnership in which
food is shared is called commensalism, which means

“eating at the same table”. Usually
*ij| one partner benefits and the

other is neutral. Animals
that raid our rubbish bins,
such as foxes, possums, and
raccoons, have this kind
of partnership with us.

Shell of a

common

whelk

(Buccinum

species)

MUTUAL PROTECTION
Acacia ants (PseucLomynnex species)
protect the bull’s horn acacia tree
{Acacia comigera) in Costa Rica.
They bite animals that try to eat
parts of the tree. In return, the tree
provides the ants with a safe place
to nest inside its large thorns. It
also produces parcels of a sweet
substance that the ants eat.

The anemone filters food
from the water. It can also
pick up scraps of food
dropped by the crab.

The hermit crab f

brings its head, f

antennae, front /
claws, and first two /
pairs of legs out of '
the shell when it is moving about.

Protection in

EXCHANGE FOR FOOD
Hermit crabs do not have their own hard shell.
They live in the empty shells of dead shellfish. As a
crab grows, it moves on to a larger shell. Some sea
anemones live on the shells inhabited by hermit
crabs. The crab carries the anemone to new
feeding grounds and provides it with leftover
scraps of food. In return, the anemone’s stinging
tentacles protect the crab from attack.

A remora’s suction
disc has a series
of plates.

BOTH PARTNERS GAIN

The red-billed oxpecker (Buphagus

erythorhynchus ) climbs over the skin
of large African animals, such
as giraffes, searching for ticks
and blood-sucking flies to eat.
The giraffe (draff a
Camelopardalis) gains
b ecause hie oxpecker
takes away

irritating pests.

The partnership between
an oxpecker and a giraffe is
an example of mutualism.

ONE PARTNER GAINS, ONE LOSES
The dodder (Cuscuta species) is a parasitic plant. It
lives on other plants, taking food from them. The
other plant therefore docs not get enough food.
Dodders do not have any green colouring, necessary
. for photosynthesis, because they do not need to
photosynthesize and make their own food.

4 The roots of the dodder Close-up photograph

penetrate into the other of a cross-section
plant’s tissue. through the stem of

the host plant, showing

1' , - /' the parasite.

Pink threads
of dodder

Remora

ONE PARTNER GAINS
The remora is a type offish. It
has a suction disc on top of its head
with which it attaches itself to
sharks. It is then protected by the
shark and picks up scraps of food
the shark drops in the water. The
remora does not do much for the
shark, although it may remove
parasites from its body.

Stem of
host plant

Find out more

Flc

) WE RING PLANTS P.318
LLYFISH, ANEMONES,

AND CORALS P.320

Fish p.326

WNS AND CITIES P.397

ECOLOGY

Colour and camouflage

Hoverflies are
harmless, but
they look like
bees or wasps
which makes
predators
think they
can sting.

Animals and plants look the way

they do for a reason. Plants have bright
colours that attract animals, which then
carry the plant’s pollen or seeds away
to make new plants. Animals have
bright colours that attract a mate or
warn that the animal is poisonous.
Dull colours camouflage, or hide,
animals against their background.
This helps hunting animals to creep
up on their prey, and helps prey to
hide from the hunters.

The wings of the male common blue butterfly
are bright blue on top which attracts a mate.

Survival

Some animals and plants
need to be noticed; others
need to hide. All living things are
a particular colour, pattern, or shape
to help them survive.

of the privet
hawk moth (Sphinx
ligustri) is bright green
with diagonal stripes. This
helps it hide on the privet
leaves on which it feeds.

The bright
colours of
ladybirds warn
predators that they
taste nasty.

HENRY
WALTER
BATES

English
naturalist and
explorer Henry
Bates (1825-92)
studied camouflage in animals.
He suggested that some
harmless insects looked like
unpleasant ones so that
predators would not attack them.
This is now known as Batesian
mimicry. He suggested that
mimicry was the result of
evolution by natural selection.

CHANGE OF COLOUR
Some animals change colour
with the seasons so that they
are camouflaged all year
round. The stoat (Mustela
erminea) is brown and black
for most of the year. In winter,
in places where it snows, the
stoat turns white, except for
the black tip of its tail.

The wings of the common
blue butterfly
(Polyommatus icarus)
are dull underneath
for camouflage on
some plants.

The bright
flowers of
foxgloves
attract

bumblebees,
which feed on
their nectar.

The bees also
collect pollen,
some of which
pollinates the next
flower they visit.

SPOTS AND STRIPES

Patterns, such as spots
and stripes, help to break
up the outline of an
animal’s body. The
leopard and bongo can ^ _

be hard to see in the Clouded leopard (Boocercus
shadows of the forests (Neofelis nebulosa) euryceros)
where they live. Some
young animals have spots
or stripes when the adults
do not. This camouflages
them until they can
defend themselves or run
away from danger.

COLOURFUL MALES
Male birds of many species are
more colourful than the females.
Females usually have to sit on the
nest and look after the chicks, so
bright colours would make it easy
for predators to see them. The
male frigate bird (Fregata minor)
has a red throat pouch. During
courtship, he puffs out his pouch
to impress a female.

Find out more

Evolution p.308
Flowering plants p.
Arthropods p.322
Birds p.332
Feeding p.343
Senses p.358

318

380

ECOLOGY

Migration and hibernation

When food is hard to find, in cold,

hot, or dry seasons, many animals migrate,
k or move to another place, to find food
^ and water. Other animals find a safe

■ place, such as a burrow or cave, and go

into a deep sleep for many months.
WT This sleep is called hibernation. Before

■ migrating or hibernating, animals eat as

much as they can to build up extra
reserves of fat in their body. In this way
they can survive long periods without
food. Migrating animals also feed when
M they can during the journey.

Serengeti National

'A3S£ i Park, Kenya

Annual rainfall
is greatest
farther
north ..

. . Migration

Animals migrate to find food, warmth, water, space, or a safe
place to raise their young. The champion long-distance
migrators are birds, such as the Arctic tern, and butterflies. In
the African dry season, wildebeest (Connochaetes taurinus)
move in their thousands to find fresh grass to eat. They follow
their parents, but many animals have to make the first
journey on their own. Then they remember landmarks or the
position of the Sun or stars. Some sense the Earth’s magnetic
field. Fish and whales may recognize ocean currents.

IS WILDEBEEST

JOURNEY

I/4 ft Migrating animals

^ can cover

^ thousands of

kilometres. In the wet
W season, wildebeest

• graze on the south-

eastern plains in Kenya, but
in the dry season they go west
and then north to areas of greater
rainfall. They return south again when the rains
bring the dry grasslands there back to life.
Predators of wildebeest, such as lions, have to
follow them, othenvise they would go hungry too.

Temperature.

Direction of
wildebeest
journey

Breathing rate

Feeding before Deep Awake for a Asleep
hibernation hibernation short time again

Hibernation

Body processes slow down in hibernation, so the
animal is just alive. Body temperature falls to a few
degrees above the air temperature, and there are
fewer, weaker heartbeats. This chart shows a
hibernating dormouse (Muscardinus avellanarius ).

SURVIVING DROUGHT
ingf ish live in swamps where the water
lisappears during the dry season. They
survive by burrowing in the mud and
curling up inside a cocoon of wet,
mucus. This stops their body losing
too much water by evaporation. The
lungfish breathes through a mud lid
to its cocoon. When the rains return,
the lungfish breaks out and swims
off. This kind of hibernation, in hot,
drv conditions, is called aestivation.

LENGTHS OF HIBERNATION
Marmots, such as this yellow-
bellied marmot (Marmota
flaviventris ), are called true
hibernators. They remain
inactive during hibernation
otherwise they would lose too
much energy. Some animals,
such as bears, are inactive for
long periods. But their
heartbeat hardly slows at all
and, if there is a warm spell,
they wake up and feed.

After

hibernation

South American lungfish
(Lepidosiren paradoxus)

Find out more

Strug

rURE OF THE EARTI
Seasons p.243
Climates p.244
Nutrition p.342
Factfinder p.424

i p.212

381

ECOLOGY

Shoreline

POLAR and TUNDRA LANDS

Fort

Yukon

Antarctic

World distribution of Polar and tundra lands

Tundra At THE TOP AND BOTTOM of the world are some of

region

the harshest ecosystems on Earth. The region around
the North Pole is called the Arctic, and the region
around the South Pole is called the Antarctic. The
Antarctic is the coldest region on Earth. Temperatures
can be as low as -80°C (-112°F) and the wind can blow at
320 km/h (200 mph). There is not a large variety of life,
region so food webs are simple and can be easily upset. The
wildlife is adapted for surviving the climate.

Polar lands

A huge area around each Pole is covered by ice. In the Arctic, the ice
floats on top of the sea and is often only a few metres thick. In the
Antarctic, the ice is on top of a rocky landmass and in places is
about 4 km (2.5 miles) thick. Animals survive the cold because they
have thick fur, dense feathers, or layers of fatty blubber under the
skin. All these help to stop body warmth escaping. Large numbers
of birds, such as penguins and eider ducks, migrate to
the Polar regions in summer. There are few
predators and plenty of
food at this time of year.

Ice floating
on the water

WALRUS

Tough skin and thick layers of fat protect
the walrus ( Odobenus rosmarus) in
the Arctic against the cold
and from attacks by
other walruses. The
length of a walrus’s
tusks may indicate its
status in the group.
It uses its tusks to
dig up shellfish
from the seabed.

ARCTIC TERN
Arctic terns (Sterna paradisaea)
raise their young in the Arctic
summer, then migrate to the
other end of the world for the
Antarctic summer. They see more
hours of daylight than any other
living creature.

sv5

WHITE WHALE
The beluga, or white whale, ( Delphinaplerus
leucas) may stay in Arctic waters all year
round, although most whales only visit the
Arctic in the summer. Belugas feed mainly on
fish such as cod, halibut, and haddock.

Icebergs broken off
the main ice pack

Monthly temperature and rainfall in
Fort Yukon, Alaska

Temperature

50 (122) r -

C(°F)

Rainfall - cm (in)

16(6)

30(86)

20 ( 68 ) j

12 (4.7)
10(3.75)

10(50)

8(3)

6 (2.36

10 (14)

-20 -4

2 (.79)

CLIMATE

The Polar and tundra regions are very
cold. There is little rain or snow because
the cold air cannot hold much moisture.
Less snow falls around the Poles than rain
falls in the Sahara desert. In winter, the
Polar regions are dark all the time and, in
summer, the Sun shines for 24 hours.

POIAR BEAR
Thick fur and layers of blubber help to keep the
polar bear ( Thalarctos maritimus) warm in the
Arctic. The blubber is a source of energy. Male
polar bears may hunt seals all through the winter.

40(104) -

14 (5.5)

382

KCOLOGY

Reindeer moss -_

(Cladonia species)
absorbed
radioactivity from
the air.

Tundra lands

The tundra is a barren landscape
on the edge of the North Polar
ecosystem. The ground is covered with
lichens, and small bushes that grow in
low, dense cushions out of the wind.

The plants have small leaves that stop
them losing too much water. In
summer, insects such as mosquitoes
and blackflies hatch from eggs laid in
the soil. The insects feed on the blood
of large mammals, such as reindeer,
and are themselves eaten by birds.

MUSKOXEN

_ Musk oxen (Ovibos moschatus) live in the Arctic

tundra. They have a woolly coat, and thick
layers of fat. In winter they grow a long
/ \ overcoat of windproof hair. The oxen

/ \ huddle together, with the young in

the middle, for warmth and
protection from predators.

POLLUTION CHAIN
In 1986, there was a serious
nuclear accident at a power station
in Chernobyl in the Ukraine. The
air was polluted with massive doses
of dangerous radioactivity which was
absorbed by plants and passed on in
the food chain. For example,
radioactivity in a lichen called
reindeer moss was passed on to
reindeer and then to humans.

Reindeer {Rangifer
tarandus) ate the lichens,
making their meat unfit for
the Lapland people to eat.

W& EIDER DUCK

In the summer the eider
duck (Somateria mollisima)
migrates to the Arctic to
nest. The female plucks
f eathers f rom her breast ™

to line the nest and keep
the eggs from losing heat.

STUDYING THE OZONE
Scientists go to the Arctic and
Antarctic to study the ozone layer.
They perform ground and balloon-
based experiments to test the air
for pollutants, and for the amount
of ozone. The ozone problem is
bad over the Poles because of the
extreme weather conditions. High
levels of ultraviolet rays are getting
through to the Earth, and harming
plankton in the sea, so disrupting
the start of many food chains.

We A little way
below the
me surface of the
Hr tundra is a frozen
W layer, called

■ permafrost, which
never thaws out. The
soil above the
permafrost thaws in
summer but the water
cannot drain away. It
collects on the surface,
forming marshy pools.

PENGUINS

Penguins live only in the Southern
Hemisphere. They cannot fly, but
are excellent swimmers, using their
wings as flippers. They come
ashore to lay eggs and to raise their
young. Some, such as these Adelie
penguins (Pygoscelis adeliae ), march
over 350 km (220 miles) from the
sea to reach their nest site.

Find out more

NORWAY LEMMING
Lemmings, such as the Norway
lemming (Lemmus lemmus), spend
most of their time sheltering among
plants or in a burrow just under the
soil. In winter, they tunnel beneath
the snow, which acts like a blanket
and keeps out extreme cold. The
number of lemmings rises and falls,
and peaks about every four years.

Nuclear energy i\136
Seasons p.243
Climates p.244
Transport in plants p.341
People .and planet p.374
Food chains .and webs p.377
Migration .and hibernation
p.381

383

ECOLOGY

Rocky

Mt Kenya

Alps

MOUNTAINS

Mt Everest

Andes

World distribution of major mountains

The lammergeyer, or
bearded vulture,
(Gypaetus barbatus)
soars on rising
currents of hot
air near
the

peaks.

Snow and rock
where nothing
can live

OoiNG UP A MOUNTAIN is like making a journey across the
Earth from the Equator to the Poles. You go through all the
main ecosystems, from forests on the lower slopes to
grassland, tundra, and snow. The wildlife of the higher
slopes has to cope with freezing temperatures, fierce
winds, and thin air. Plants grow in dense cushions and have
thick, hairy leaves that trap heat and reduce water loss.

Wingless insects are common because the winds are too strong
for insects to fly. Some mountain mammals have large hearts and
lungs to help them get enough oxygen from the thin air. They may
also have thick fur to keep out the cold. Some animals turn white
in winter, for camouflage in the snow and ice.

Snow leopards
(Panthera uncia)
have a thick coat,
keeps

Snow line

Tree line

Tundra - bare
rock and
frozen soil

Takins (Budorcas
taxicolor) have
strong legs and
large hoofs -
used to climb
the steep
slopes.

Mount

Kenya

on Equator

Himalayas

30° north
of Equator

Alps

45° north
of Equator

Arctic

70° north
of Equator

TREE LINE
The height above which it
is too cold and windy for
trees to grow is called the
tree line. The snow line
is the lower edge of the
part where snow stays
all year round. The
height of the snow
and tree line depends
on the weather and
how near a mountain is
to the Equator.

Alpine grassland -
rich in flowers and
insects in summer

Low-growing shrubs
rhododendron,
juniper, dwarf birch

The red panda
(Ailurus fulgens) is
a good climber.

The wild ass, or
onager, (Equus
hemionus) lives
on the high
grassland in
summer but
moves down to
lower levels in
winter.

Cool coniferous
forest - cedar,
pine, fir

THREATS TO MOUNTAINS

Mountain ecosystems are not as
threatened as many others. Many
mountains are the last refuge for
rare species. But some mountain
forests and scrublands are being
destroyed by the construction of
ski resorts. Unique alpine plants
and fragile soils have
to be cleared away to
make ski runs, and
new roads and
holiday villages
can upset
the natural
mountain life.

Mountain

ZONES

All mountains have broad
bands, or zones, each with its
own typical plants and animals.

In the Himalayas, on the border
of Nepal and India, the bottom
zone is a warm deciduous forest.

Above this is a band of cooler
coniferous forest. The tree line is at
about 3,400 m (11,200 ft). Higher than
this, there are only low-growing bushes
and shrubs, which merge into grassland and
bare rock just below the snow-covered peaks.

Himalayan langurs
(Presbytis entellus)
move up and down
the mountain as
seasons change.

Temperate
deciduous
forest - oak,
rhododendron

Sub-tropical
deciduous
forest -
sal, arjun,
teak trees

Find out more

Climates p.244
Snow p.266
Conifers p.317

Colour and camouflage p.380
PoiAR AND TUNDRA LANDS P.382
Grasslands p.392
Temperate forests p.396

384

ECOLOGY

Seashores

Acorn barnacle }
|palanus %
Kalanoides). jja

\Rough

periwinkle

(Littorina

saxatilisk^

Middle shore

Readlet anemnnt

actinia equina]

Bladder wrack

Sca rlet stajdish
(Henricia oculata)

(Fucus vesiculosus)

Oarweed

(Laminaria

digitata)

Common sea squirt
(Ciona intestinalisL

Lower shore

Where THE LAND MEETS THE SEA there is an ecosystem
rich in food. Some food is washed down by rivers; more is
brought in from the sea by the tides. Animals and plants are
adapted to survive these difficult conditions. The environment
is constantly changing as waves and tides move water, sand, and
pebbles up, down, and along the beach. When the tide goes
out, the plants and animals are exposed to air, winds, strong
sunlight, and rainwater. On tropical and polar shores, the
animals and plants have to tolerate extreme temperatures.

Seabirds such as shags
(Phalacrocorax aristotelis)
and puffins (Fratercula
arctica), far right, nest
on cliffs where they
are safe from
enemies.

ESTUARIES

The place where a river meets the sea is
called an estuary. Birds known as waders,
such as these redshank (Tiinga totanus ), walk
through the shallow water searching for food
in the mud with their long beaks. Estuaries
are important to migrating birds in
winter. Many birds break their journey
to rest and feed there.

During the day,
the masked crab
(Corystes cassivelaunus)
stays under the sand. It
breathes by taking in water
through its tube-like antennae.

Only the tips of these stick up
into the water.

Shifting sands

Beneath the surface of a sandy beach is
a mass of worms and shellfish. There
they are protected from pounding
waves and drying air. Many sandy
shore animals filter fragments of food
from the sand and the seawater.
Microscopic algae coat the surface of
the sand or float in the water.

Uppe r shore

Channelled
wrack
(Pelvetia

Thin tel I ins
(Tellina tenuis) burrow in the
sand from the middle shore to
shallow water. They suck in
food from the seabed using a
siphon like a vacuum cleaner.

Lugworms
(Arenicola marina)
live in a U-shaped
burrow under
the sand.

Limpet (Patella
intermedia)

THREATS TO SEASHORES

Beaches can be at risk from people
building hotels and airports,
dropping litter, and dumping oil
and sewage into coastal seas. Birds
and reptiles that nest on beaches
are disturbed by the noise and
bright lights in tourist areas.
Loggerhead turtles (Caretta caretla)
come ashore to lay their eggs on
the beaches of the Greek island of
Zakynthos. Their numbers
have decreased but
naturalists are now
protecting their
nesting sites.

Young loggerhead turtle

ROCKYSHORE ZONES
Zones on a rocky shore are often
clearly marked by the types of
seaweed. Green seaweeds grow near
the top of the shore, and brown ones
grow near the lower shore. Different
animals also live in each zone,
according to the amount of time
they can survive out of the water.

Find out more

Shoreline p.236
Migration and hibernation
p.381

Oceans p.386
Rivers and iakes p.388
Fact finder p.424

Puffin

The roots of marram
grass (Ammophila
arenaria) spread out
under the sand in a \

thick network which
holds the sand yy
together. | Tpj

385

ECOLOGY

North

Atlantic

Ocean

Arctic

Ocean

Oceans

More THAN 70 PER CENT of the Earth’s surface is
covered by ocean. This makes the oceans the largest
ecosystem. Life exists at depths of 4 km (2.5 miles) or
more. Dead plants and animals, food scraps, and
droppings fall down on the ocean floor, making it rich
in nutrients. There are many different habitats in the
oceans, from sandy underwater deserts and huge
mountains to coral reefs and open water. The oceans
do not contain a great variety of species - only about
20 per cent of the Earth’s species live there, and nine
out of ten of these live on the ocean floor.

PLANKTON

Most ocean food chains start with the
microscopic plankton in the enphotic
zone. Tiny plants (phytoplankton), such
as diatoms, are eaten by tiny animals
(zooplankton). Zooplankton include a
large number of larvae of animals such as
shrimps and crabs. They provide food for
a variety offish, which are in turn eaten by
other fish and marine mammals.

There are more
phytoplankton in cooler
oceans as there are
more nutrients, such as
phosphorus and
nitrogen, which are
needed for
photosynthesis.

The oceans are
linked and animals
can move between
them. One species
may fill the same
niche worldwide.

Ocean zones

There are two main habitats in
the ocean - the water itself,
called the pelagic habitat, and
the ocean floor, called the
benthic habitat. The pelagic
habitat is divided into several
depth zones. Sunlight reaches
down through only about 100 m
(330 ft) and in very muddy waters it
may reach down less than a metre.
This thin zone, where plants can
photosynthesize, is called the
euphotic zone. Below this, down to
about 2,000 m (6, 500 ft), is the
bathyal zone, where there is little or
no light. The vast ocean deeps, or
abyssal zone, go down to 6,000 m
(19,500 ft) and more.

DEEP-SEA CHEMICALS
On the floor of the Pacific Ocean
there are cracks in the Earth's crust
where hot, sulphur-rich water
gushes out of tall vents. Animals
live nearby, absorbing chemicals
dissolved in the water. Bacteria in
their body tissues convert the
chemicals into the energy that

the animals need. v

The food chain
near the deep-
sea vents
begins with
bacteria that do
not need light for
photosynthesis.

Giant worms (Riftia
pachyptila) up to 3 m

Deep ocean trenches
are called the hadal
zone. The deepest
known trench is the
Marianas Trench in
the Pacific Ocean. It is
11,034 m (36,201 ft)
deep. Mount Everest
would fit inside it.

Sperm whales (Physeter catodon)
feed mainly on squid and can dive
to at least 1,000 m (3,300 ft)
in search of their prey.
Their sonar system is
very useful for finding
food in the black
ocean depths.

FINDING FOOD
Food is hard to find in the
dark ocean depths. Deep-sea
fish, such as this angler fish
(Mela n ocoelus johnson i ), cai i
have lights that attract prey,
and large stomachs to hold as
much food as possible.

(10 ft) long live near
the deep-sea vents.

ECOLOGY

CORAL REEFS
The Great Barrier Reef of Australia is
the largest coral reef in the world.

Coral reefs contain a great variety of
wildlife. The waters are not rich in
nutrients but the reef inhabitants
recycle them very quickly so that
nothing is wasted. Corals can live only
L in clean, warm, salty water less than
^30 m (100 ft) deep, so that sunlight
A reaches them. Algae live in the
bodies of the corals and they need
H sunlight to make food. Coral reefs
are threatened by pollution,
^mining, and rising sea levels due to
the greenhouse effect.

|k JACQUES-YVES

cousteau

IP Frenchman Jacques

Cousteau (born

: 1910) is famous for

his underwater

9 explorations. In the

early 1940s, he
developed the
aqualung, a portable
breathing apparatus for
divers, with the French engineer Emile
Gagnan. This encouraged more people
to explore the oceans, which has greatly
increased our knowledge of underwater
life. Cousteau helped to develop an
underwater camera, and has made
many films of life under the sea,
including The Silent World.

Cousteau has also campaigned
to stop mining
in Antarctica.

Corals are tiny animals that filter
food from the water with waving
tentacles. Skeletons of coral can
build up to form a
<fj/^ branched coral or a
V w coral mound.

The shallow waters near
continents are rich in
nutrients because they
are washed off the land,
and storms mix up the
water, bringing nutrients
to the surface.

Most of our fishing is done in shallow
waters near the edges of continents.

A coral reef is built
up over thousands
of years from coral
skeletons.

A narrow ledge of land called the continental shelf sticks
out from continents under the oceans. The shallow water on
the continental shelf is called the neritic (nearshore) zone.

THREATS TO OCEANS i

The biggest threat to
ocean ecosystems is
pollution from oil, sewage,
and industrial waste.

People also hunt fish, w

whales, and other wildlife.

As the number of people in
the world grows, so more
food is needed. In some places,
there are no more fish left to
catch. Strong nets stretch for up
to 60 km (37 miles) across the
oceans. With these nets and new
technology to find fish, they have
little chance of escape. But some
countries have set limits on how
many fish can be caught. Others
use nets with large holes so that
young fish can escape and grow
into the next generation.

OCEAN MAMMALS
The largest animals on Earth,
whales live in the oceans where
the water supports their massive
bodies. They are mammals so
although they can stay underwater
for a long time, they have to

Herring
numbers
have fallen
dramatically in
the last 20
years.

come

to the surface to breathe air. They
blow out the used air through
nostrils on top of their head, called
spouting, then take in fresh air.

SHOALS OF FISH
Fish such as mackerel
(Scomber scombms), swim
near the surface in
shallow waters. They Filter
small pieces of food from
the water with their brush¬
like gill rakes.

Find out more

Sulphur p.45
Seas and oceans p.234
Single-celled organisms p.314
Jellyfish, anemones, and
corals P.320
Fish p.326
Mammals p.334
Photosynthesis p.340
Feeding p.343

387

ECOLOGY

Rivers and lakes

The STILL WATERS OF TINY POOLS and great
lakes, and the flowing waters of mountain streams
and wide rivers, are all freshwater ecosystems. Some
of these change with the seasons; others are
changing all the time. The weather and natural
processes, such as erosion, affect the amount of
water in each area. Rivers change their course and
new lakes form. They can also fill up with silt,
material deposited by the water, and turn into dry
land. Some pools and rivers appear only in a wet
season, so only simple communities live there.
jfe But large rivers and lakes contain

complex communities that have
K. developed over hundreds of years.

\ The horse
leech

1 (Haemopis
san 9 u i su g a )
clings on to
Wm stones with
Jr suckers. It eats
insect larvae,
snails, and worms.

Fast mountain stream

/ - Brown trout

(Salmo trutta) like

|f 0001 water with plenty

of oxygen. They are
good swimmers and can
move easily against the strong currents.

Adult dragonflies
lay their eggs
on plants, and
the larvae, called
nymphs, live in
the water until
they change
into adults.

Water plantain
(Alisma plantago-
aquatica) provides
shelter for birds. It
grows up to 1 m
(3.3 ft) tall.

Young swift river

The Eurasian kingfisher (Alcedo atthis)
nests in holes in the bank. It dives into the
water up to 100 times a day to catch fish.

From source to sea

In fast-flowing water near the source
(the start) of a river, there is plenty of oxygen but few
plants for animals to eat. Most food chains start with
dead material in the water. In the middle part of the
river, the water flows more slowly. Plants take root and
provide food and shelter for animals. The water in the
lower part of the river, towards the sea, can be muddy. It
flows slowly and contains less oxygen. Vertebrates, such
as fish, are an important part of the community.

Slow mature
river

The otter (Lutra lutra) has
webbed feet to help it
swim underwater. It
can close its ears to i

stop water getting in. '

Greater reed mace (T ypha
latifolia) grows over 2 m
(6.6 ft) tall. It can survive if
the water level rises.

Dams are built
across rivers to
provide water, to
generate
electricity, or to
stop flooding.
Villages and
farmland can be
covered by lakes
that are formed.

TROPICAL RIVERS
The black caiman
(Mdanosuchus niger )
3 : lives in the Amazon
in South America. It
- ~***H§5* is related to crocodiles
and alligators. It is the top
v* carnivore in its ecosystem,
eating everything from fish to
wild pigs. Hunting by humans means
it is now in danger of extinction.

RECORD-BREAKING IAKE
Lake Baikal, in Siberia, is the
deepest and oldest freshwater
lake in the world. It reaches a depth
of 1,620 m (5,314 ft) and is at least
25 million years old. The lake contains
more than 1,000 species of animals that
are found nowhere else in the world.
Sadly, this ecosystem is threatened
by pollution from factories,
towns and agriculture ^0

around the lake.

THREATS TO RIVERS

When dams are built across
rivers, huge lakes are formed
and the nature of the river is
changed. The lakes provide a
new habitat for fish, but make it
difficult for some other animals
and plants to survive. The Aswan
dam, across the Nile in Egypt,
also stops silt flowing down the
river. The silt used to flood over
the land and enrich the soil.

Find out more

Wfathkring and erosion P.230
Rivers p.233
Worms p.321
Arthropods p.322
Fish p.326
Reptiles p.330

Food chains and webs p.377

388

ECOLOGY

Wetlands

[Taxodium distichum)

Six PER CENT OF THE EARTH’S SURFACE is covered by
wetlands. They can be fresh or saltwater, and include wet
grasslands, called marshes, wet peatlands, called bogs, and
waterlogged forests called swamps. Wetlands are some of the
world’s richest ecosystems. They produce more plant material
than most other ecosystems on Earth. A variety of small
mammals, birds, insects and other invertebrates live there.
Birds flock to wetlands to nest because they do not have many
enemies there. Large mammalian
predators would sink into the wet
ground. Water levels change
with the seasons so the
wildlife has to be able to
survive in dry and
wet conditions.

Stunted bald cypress

The manatee is a mammal
so has to breathe air, but it
can stay underwater for up
to 15 minutes.

Sawgrass dotted

with islands of trees *. e r-

SITATUNGA
Long splayed-out
hooves stop the
sitatunga

(Limnotragus spekei)
from sinking into
the swampy ground
of Af rica. The
sitatunga can swim
well and, in times of
danger, hides underwater
with only the tip of its nose
showing, so that it can breathe.

The zebra butterfly
(Heliconius charitonius)
flies slowly on long,
narrow wings. At night,
large groups gather on
bare twigs.

Slash pines (Pinus elliottii) and
saw-palmetto (Serenoa repens)
grow on higher ground.

The American darter (Anhinga
anhinga) dives underwater to catch
fish. It then perches with its wings
half-open to dry them in the sun.

Mangrove swamp on
the coast

THE EVERGLADES

At the southern tip of Florida in the
United States is a huge area of
cypress swamp called the Everglades.
It is home to rare species such as the
manatee (Tricheus manatus) and the
Florida panther (Felis concolor coryi ).

It is now a national park but is
threatened by chemicals used in
agriculture, and by drainage,
pollution, and tourism. Fast boats kill
more than 100 manatees every year.

The American alligator
(Alligator mississipiensis) is
the largest and loudest reptile
in North America. In the
spring, the male bellows to
attract females.

2 Key

Water
Swamp peat

Lake clay O
Lake mud 4^
Peat

The garpike -
(Lepisosteus
osseus) has gills
for breathing underwater,
but can also breathe air if
the water dries up.

The water moccasin
(Agkistrodon piscivorus)
is a poisonous snake
that hunts at night.

MANGROVES

The most common trees in
tropical fresh and saltwater
swamps are mangroves. They
can survive in waterlogged
mud because they have
breathing pores in their
roots. Some mangroves have
roots that grow up into the
air and get oxygen. The red
mangrove (Rhizophora mangle)
grows in coastal swamps and
estuaries. It protects them
from storms and tidal waves.

HOW A PEAT BOG FORMS 4
A peat bog may form where a lake
fills in with mud and plants. (1) The
water is clear, with mud on the
bottom. (2) Mud collects around
roots of plants. (3) Mosses grow and
build up mounds of peat. (4) The
lake disappears and is replaced by a
dome of peat. Peat bog forming is
an example of succession.

Find out more

WlL

Pressure p.127
Reptiles p.330
Mammals p.334
IIE BIOSPHERE P.37
DIJFE IN DANGER P

.398

389

ECOLOGY

Deserts

Great Basin
Mojave

Gobi

Thar

Arabian

Great

sandy

Atacama

Great

Victoria

Sahara

Gibson

World distribution of major deserts

Deserts are the driest places on Earth.

Most have less than 10 cm (4 in) of rain a year.
Some may have no rain at all for several years. Most
deserts are hot, so more water evaporates into the
air than falls as rain. Desert plants have deep or
wide-spreading roots, tough skins, small leaves or
spines, and special ways of storing water. Many
animals may never drink, getting all their water
from their food. Only a few species of plants
and animals can survive in the desert so there
is little dead material to make the soil rich.

The few nutrients that are present take a
long time to cycle through the ecosystem.

Desert by day

Daytime temperatures
in hot deserts may reach

more than 50°C (120°F) and the surface of the sand can be as
hot as 90°C (195°F). Most animals hide away in burrows or
beneath rocks where the air is cooler and more moist. Some
desert plants have hairy leaves that reflect strong sunlight. The
pores of most stay shut during the day so less water escapes.

Chuckwallas
(Sauromalus obesus)
bask in the morning sun
until they are warm enough
to crawl off in search of
flowers, fruits, and seeds to eat.

The huge
ears of the
fennec fox
(Fennecus
zerda) help it to
hear the faintest
sound of prey
moving nearby.

The ears also help
the fox to keep cool
by giving off heat
like a radiator.

CONVERGENT EVOLUTION
Animals living in similar habitats
in different parts of the world often
look similar, for example, the kit fox of
North America and the fennec fox of Africa.
This is because both foxes have adapted to
survive in the same kind of ecosystem,

The kit fox
(Vulpes macrotis)
comes out at night
to hunt. It runs
fast to catch small
animals before they
escape down a burrow.

On its powerful back legs, the
black-tailed jack-rabbit (Lepus
californicus) can leap away
from danger at speeds of up
to 56 km/h (35 mph).

Kangaroo rats (Dipodomys deserti)
get all the water they need from
the seeds they eat. They carry
seeds back to their burrow in
cheek pouches.

where environmental conditions are similar.

This is called convergent evolution.

STORAGE TANKS

Desert plants and animals
have to survive long dry
spells. Some animals can
store fat in their body. The
fat can be broken down to
provide energy
and water.

The gila
monster
(Heloderma
suspectum)
stores fat in its
thick tail to help
it survive hard
times.

A camel, such as the one¬
humped Arabian camel
(Camelus dromedarius), can
go without water for weeks. A
camel can drink up to 114 litres
(25 gallons) of water in one go.

Because water
is lost through
leaves, cacti such
as this Mammillaria elongata
do not have any - just
spines, which prevent them
from being eaten. They store
water in their thick stems.

SIDE¬
WINDING
Several snakes
that live in sandy
deserts, such as this sidewinder adder (Bilis
peringueyi ), move by throwing themselves over
the sand in “S”-shaped curves. This is called
side-winding because the snakes travel sideways
rather than forwards. The advantage of this
type of movement is that only two parts of the
snake’s body touch the hot surface of the sand
at any one time. The snake also is less likely to
sink into the soft sand.

390

ECOLOGY

The world’s smallest owl,
the elf owl (Micrathene
whitneyi), hides away by
day in holes made by
woodpeckers in
cactus stems.

The cactus wren
(Campylorhynchus
brunneicapillus) builds
its nests in cacti, where
its young are well
protected from
enemies by the
sharp spines.

Desert at night

At night, the desert is much cooler
and the air becomes more moist.
Many animals come out to hunt
and the desert comes to life. Food
is still hard to find, and many
desert hunters, such as spiders and
scorpions, are very poisonous. If a
meal does come their way, they
have to deal with it as quickly as
possible and must not let it escape.

Saguaro cacti (Cereus
giganteus) have thick
rubbery “skin”. They soak
up water using a wide-
spreading network of
shallow roots.

Temperature - °C (°F)

50(122) -

Rainfall - cm (in)

16(6)

14 (5.5)
•12(4.7)
10(3.75)
8(3)

6 (2.36)
4(1.6)

2 (.79)

JFMAMJJASOND

Monthly temperature and rainfall in Aswan, Egypt

40 (104)
30 (86)
20 (68)
10 (50)
0(32)
-10(14)
-20 (-4)
-30 (-22)

The spotted skunk
(Spilogale putorius)
comes out mainly at
night to hunt for small
animals, eggs,
insects, and fruit.

Scorpions use the poisonous sting at the tip of the
tail to defend themselves and kill their prey. This is
an Arizona scorpion (Centruroides sculpturatus).

CLIMATE

The largest deserts are near the Equator. They
are hot and dry all year round because the winds
that blow across them contain very little moisture.
Deserts in colder parts of the world, such as the
Gobi desert in central Asia, are hot in summer
and cold in winter. Deserts also occur in the
shelter of high mountains, such as the Atacama
desert in South .America.

Creosote bushes (Larrea tridentata)
grow evenly spaced out because the
roots of each plant use up all the water
and nutrients in the
soil around it.

Western spadefoot toads
(Scaphiopus hammondi)
appear only at night. They
use hard “spades” on their
back feet to dig burrows.

The desert tarantula
(Aphonoplema chalcodes)
is a poisonous spider that
spends the day hidden in
a burrow.

A chuckwallah spends the
night sheltering under a rock,
and becomes active by day.

The water in an oasis comes
from a rainy climate many
kilometres away.

Oasis

OASES

In a few places in a desert, water
seeps through the ground to form
a moist area called an oasis where
plants can grow. Oases are a vital
lifeline for animals, including
people travelling across the desert.
The water in an oasis comes from
water-filled rocks near the surface.

It may have fallen as rain many
kilometres away and drained down
through the rocks under the desert.
But oases do not last forever; the
water may run dry or sand dunes
may be blown over the oasis. People
and animals then have to move on.

By day, the
kangaroo rat
sleeps in a
burrow, out of
the heat of the
sun. At night it
travels long
distances to
find food.

Land surface
Water-filled rock

SPREADING DESERTS

The spread of deserts is a
major threat. It is partly
caused by people who live
on the desert edges. The
grazing of animals, and
the cutting down of wood
for building, can cause the
land to turn to desert. This
is called desertification. It
is a particular problem in
areas where several years
have passed without any rain.

Oasis in Australia

Find out more

Heat transfer p. 142
C IMATES P.244
Evolution p.308
Transport in plants p.341
Movement p.356

391

ECOLOGY

Grasslands

Steppes

Harare
Savanna

World distribution of major grasslands

Food for all

The tropical grasslands of East Africa are called the
savanna. More than 40 species of grazing mammals live
here and share out the food. There is usually enough
to go round because the animals feed on different
parts of the grasses, shrubs, and trees. For example,
zebras eat the top of the grass stems, wildebeest eat the
middle part, and Thomson’s gazelles eat the bottom
part. Dik-diks concentrate on small bushes near the
ground while giraffes feed high up in the trees.

Where THE CLIMATE IS TOO DRY, and the
soils too poor for most trees, grasses grow. These
areas are called grasslands. Grass is the start of
many food chains. It is able to survive nibbling by
animals because it sprouts from the
bottom, and not from the tips as
other plants do. The more the
grass is bitten off, the more it
grows. Grass also grows back
well after fires, which are
common in this
ecosystem. In dry or
cold seasons, animals
have to migrate Ion
distances to find
enough food
and water

to survive.

Thomson’s gazelles
(Gazella thomsoni)
feed on young
grass shoots
and high-
protein seeds
at ground level.

Wildebeest eat the leafy
middle

Giraffes (Giraffa
Camelopardalis) feed on
leaves up to 6 m (20 ft)
above the ground.

Monthly temperature and rainfall in Harare, Zimbabwe
Temperature - °C (°F) Rainfall - cm (in)

50(122)

40 (104)

14(5.5)

HUNTERS

The large number of herbivores
on the Af rican savanna are food
for a whole range of predators.
Each predator tends to have a
favourite food because of the
way it hunts. Cheetahs can chase
gazelles at up to 100 km/h (62
mph) but for a short time only.
Lions cannot run so fast. They
have to get close to their prey.
But they are strong and hunt in
groups so can kill large animals
such as wildebeest. Hyenas also
hunt in groups but usually kill
animals only as large as a zebra.

Zebras feed on the
coarse, tough tops
of grasses and
also dig for roots.

Dik-diks browse on
young leaves of small
bushes, especially
acacia shoots.

12 (4.7)
10 (3.75)
8(3)

6 (2.36)

A M C\

(Acinonyx Thomson’s gazelle (Gazella thomsoni)

CLIMATE

Tropical grasslands are warm all year round, but
there is a long dry season in summer. Temperate
grasslands have very cold winters, with hard
frosts, and hot, dry summers. This graph shows
the climate for a city in a tropical grassland area.

Lion (Panthera leo)

Hyena (Hyaena species)

Wildebeest (Connochaetes
taurinus)

Common zebra
(Equus burchelli)

392

ECOLOGY

ASIAN STEPPES

Temperate grasslands called the Steppes stretch
across central Asia f rom Europe to China,
f r ; Targe herds of grazing animals, such as

bison (Bison bonasus), and saiga antelope
{Saiga tatarica ) used to graze here. They
trod seeds into the ground so that they
could grow, encouraged fresh growth by
biting off the grasses, and fertilized the
soil with their droppings. Hunting and
farming have killed most of these animals,
although saiga antelope are now increasing
due to conservation measures.

Cavies (Cavia aperea) usually shelter under
rocks or in burrows dug by other animals.
They are wild relatives of the pet guinea pig.

Many termite nests
contain corridors
and chambers
and may have
an air-
conditioning
system.

Fungus

The mar a, or Patagonian
hare, (Dolichotis patagona)
lives in burrows in groups of
up to 40 animals. It can run
swiftly away from danger,
leaping up to 2 m (6.5 ft) into
the air on its long back legs.

Burrowing

ANIMALS

On the pampas of
South America, huge
numbers of small
mammals live
underground where
they are safe from
fires and predators.

Their burrowing
helps to mix up the
soil layers and stops all the minerals
building up on the surface. This
makes the soil rich and helps the
grasses and other plants to grow. On
the North American prairies, ground
squirrels, called prairie dogs (Cynomys
species) live in huge groups and have
a whole “town” of interconnected
burrows. They keep the ground
grazed all around the burrows so that
they can see enemies coming.

Burrowing animals of the South American pampas

Hyena eats
zebra.

Zebra
eats grass
containing
nutrients
from the soil.

Hyena

eventually

dies.

THREATS TO
GRASSLANDS

Hunting has drastically
reduced the number of
grazing animals and their
predators on grasslands.
Where hunting is banned,
people still poach, or hunt
illegally. At least 85 per cent
of the worlds’s rhinoceroses
have been killed by poachers
during the last 30 years. Gamewardens such
as these in Kenya have to look out constantly
for hunters. Sometimes they rescue animals
that have been illegally trapped.

Waste material is broken
down into nutrients by
decomposers such as beetles.

NUTRIENT CYCLE
Many grassland animals, bacteria,
and fungi feed on dead plants or
animals or animal dung. Some of
the nutrients become part of the
decomposers’ bodies and some
eventually enrich the soil. This
means that nothing is wasted, and
the nutrients go round and round
in an endless cycle.

TERMITES

Insects called termites are a vital part of
decomposition in grasslands. They eat
dead material or take it inside their tall
mud nests. They use it as compost for
the fungus they grow for food. Termite
nests can be up to 2.5 m (8 ft) high and
contain up to 20 million individuals.

Viscachas (Lagostomus maximus) dig
huge networks of tunnels with their
strong front feet. They can close their
nostrils while digging, to stop soil
getting in. They come out at night to
eat grasses and other plants.

Dead material
is decomposed
and mixed with
the soil.

GEORGE
AND JOY
ADAMSON

British game
warden George
Adamson
(1906-89) worked
to protect and
conserve wildlife in
Kenya, Africa. He worked
with his wife Joy (1910-80)
who was especially interested
in lions. She is famous for
looking after the lioness Elsa
as a cub, and the story of
Elsa’s return to the wild was
made into the film Bom Free
in 1960. Both George and
Joy Adamson were murdered
in Kenya.

Find out more

Climates p.244
Nutrition p.342
Digestion p.345
Food chains and webs p.
Migration and hibernation
p.381

*.377

393

ECOLOGY

Tropical rainforests

More THAN HALF of all animal and plant
species in the world live in tropical rainforest
ecosystems. But these forests cover less than 10
per cent of the Earth’s land surface. Tropical
rainforests grow in regions near the Equator in
South America, Africa, Asia, and Australia. They
are so rich in life because they are wet and
warm, and have bright sunlight overhead - all
conditions that encourage life. The trees grow
fast and reach great heights as they
^ compete with each other to get as

much light as possible.

Rainfall - cm (in)

32 (12.6)

r 28(11)

Malaysia

Sumatra

Borneo

Papua

New

Guinea

South

America

Manaus Africa

World distribution of major tropical rainforests

The harpy eagle (Harpia harpyja) is _ 1

the biggest eagle in the world. It soars
over the canopy hunting for
monkeys and sloths to eat.

Toucans feed .
on fruit,
leaves,
and
seeds.

Temperature - °C (°F)

50(122)

LOOKING AFTER THE FORESTS
This family in the Brazilian
rainforest is making baskets from
natural materials. Over thousands of
years, rainforest peoples have lived
in harmony with their surroundings.
They grow a mixture of crops in
small areas to make the best use of
nutrients. Alter afewyears, the soil
is left to rest and recover.

Monthly temperature and rainfall in Manaus, Brazil

Spider monkeys
(Ateles species)
use their tails to
grip the branches.

CLIMATE

Rainforests are warm all year round,
with temperatures between about
20°C and 28°C (68°F and 82°F). This
is the wettest ecosystem, with rain
nearly every day. Up to 4 m (160 in)
of rain falls in a year.

Emerald tree
boa (Corallus
_caninus)

Sloths (Bradypus tridactylus) hang
upside-down in the trees, using
their long curved claws as hooks .

Layers of life

The wildlife in Amazonian
rainforests lives at different
levels. Most live near the top of
the trees, in the canopy, where
there is lots of sunlight,
warmth, and food. Below the
canopy, in the understorey, it is
darker and cooler, and wildlife
is less varied. The largest animals
live on the forest floor.

Tree frogs are common
because they can lay their
eggs in pools of water that
collect in the trees.

In the under storey,
climbing plants, such
as lianas and vines,
twine around the
trees and bushes.

Army ants move through
the forest in columns of
up to 200,000ants. They
march to find food for
their larvae.

Peccaries (Tayassu
species) feed on
plants at the
forest edge. Jjj

The spotted coat
of the jaguar
(Panthera onca)
camouflages it
as it preys on
animals such as
? agoutis and
F peccaries.

MINI ECOSYSTEM
Plants called bromeliads live on
the branches of trees. Pools of
water collect in them, creating a
mini-ecosystem. Rotting leaves and
animal droppings provide food for
bacteria and insects, which are in
turn eaten by small animals.

Fungi can
live on
the forest
floor

a 'because they

do not need light
to make their food.

Agouti (Dasyprocta species)

394

ECOLOGY

ORANG-UTAN

With their long arms and strong
lingers, orang-utans (Pongo
V pygmanis) swing quickly, hand
A over hand, through the trees.

They live in the rainforests of
Borneo and Sumatra. The
name orang-utan is a
Malysian word

^ ^^^B meaning “man of

the forests”.

BIRD OF PARADISE
fhe Raggiana bird of
t paradise (Paradisea
ftL raggiana) lives in the

WL rainforests of Papua
New Guinea. It has
short wings to fly
j through the trees
and strong feet to
' Ml grasp branches.
^B The male, shown
here, may hang
upside-down on a
B branch while he tries
W to impress females
with his brilliant-
coloured feathers.

Moving through

THE FOREST
Rainforest animals have special
features to help them move
through the trees. Birds have
short, broad wings so they can
twist and turn between the
branches. Some animals have
flaps of skin that unfold like
wings and enable them to glide
from branch to branch. Monkeys
use their hands and feet to climb
through the trees. Some can grasp
branches with their tail, too, like an
extra hand. This is called a
prehensile tail.

Rain drips down through
the trees and is taken in
through the leaves and
roots. Water that the
trees do not need is
given out through
the leaves.

FLYING GECKO
The flying gecko (Ptychozoon knhli )
lives in the rainf orests of Malaysia. Folds of
skin along the sides of its body, tail, and legs allow it to glide
from tree to tree. The folds also camouflage the gecko when it
s resting on tree bark. The gecko has ridges of scales on its f eet
and sharp claws, which help it cling to the slippery tree trunks.

Rainforest

CYCLES

Water, oxygen, minerals,
and nutrients all pass
through the trees. Due
mainly to the warmth and
moisture in a tropical
rainforest, nutrients are
recycled from the soil via the
trees to the canopy quickly.
This means that the soil is
surprisingly poor, and attempts
to farm on the land usually fail.

Oxygen is taken in
during respiration and
given out during
photosynthesis. Carbon
dioxide is given out during
respiration and taken in
during photosynthesis.

Dead leaves and animals
fall to the ground.

Bacteria and fungi in
the soil break down
the dead material. The
trees can then take up
the nutrients through
their roots and use
them to grow.

THREATS TO RAINFORESTS

Since 1945, more than half the
world’s rainforests have been
destroyed. Hundreds of species
of animals and plants are now
extinct. An area of forest the size
of a soccer pitch disappears every
second. The main threats come
from people cutting down the
trees for timber, to use the land
for cattle ranches and farms, or
to mine for oil and metals.

Find out more

STUDYING THE RAINFOREST
There are thousands of species
i of animals and plants living in
I rainforests that scientists know
nothing about. Ecologists are
I studying there all the time.
f They use mountaineering
equipment to climb up to the
canopy, and build permanent
walkways through the trees.

LUNGS OF THE PI AN FT
Rainforests are sometimes called
the lungs of the planet. Large
areas of rainforest, such as this one
in Malaysia, take in huge amounts
of carbon dioxide, and give out
lots of oxygen and water during
photosynthesis. This influences the
climate of the whole Earth.

Climates p.244
Photosynthesis i\340
Transport in plants p.341
Cycles in the biosphere p.372
Colour and camouflage
p.380

Wildlife in danger p.398

395

ECOLOGY

Woodlice (Porcellio
scaber) live in
damp, dark places
under leaves,
stones, bark, and
logs. They feed on
decaying leaves,
bark, and fungi.

Temperate fores

Conifers and broadleaved trees grow in

temperate forests. The forests are found in north temperate
regions, such as parts of Europe and North America, which
have a mild climate. There are distinct seasons, with cold
winters and warm summers, but nothing too extreme.
Conifer forests tend to grow in the north, and broadleaved
forests farther south. Temperate forests provide food and
shelter for a large number of plants and animals. More light
reaches through the trees than it does in a rainforest
because the trees are not as tightly packed. Small plants can
survive without having to grow as creepers up trees to get
sunlight. In colder areas, it can take years for dead material
to be broken down, so the cycles of nutrients are slower.

Oak marble galls form when
gall wasps (Andricus kollari)
lay their eggs on the buds of the
oak tree in spring. Larvae
develop into adult wasps inside the
galls and eat their way out in autumn.

Oak tree ecosystem

An oak tree is a broadleaved
tree. It is an ecosystem on its
own. It makes its own food, and its
leaves, flowers, fruit, bark, and wood
are eaten by insects, birds, and small
mammals. These creatures are in
turn eaten by bigger animals. All the
animals eventually die and rot back
into the soil. The nutrients in their
bodies are taken up by the tree again
and used for growth. The ecosystem
changes with the seasons as the tree
sprouts leaves in spring and drops
them in autumn. In winter the tree
rests and the animals hibernate,
migrate, or become less active.

The beak tips of
the common
crossbill (Loxia
curvirostra) are crossed,
enabling the bird to
pine cones to
reach the
seeds
inside.

Great spotted
woodpeckers
(Dendrocopus major)
nest in holes in the tree
and chisel into decaying
trunks to search for
insects to eat.

The fruiting
bodies of honey
fungus (Armillaria
mellea) sprout from
tree stumps and dead
trees in autumn.

affects coniters,
making the
needles drop off.

CONIFEROUS FORESTS
Conifers are more common where
it is colder. Trees cannot take up water from the
frozen soil in winter. But the needles of conifers
lose less water than broad, flat leaves, so they can
stay on the trees all year round. The pyramid
shape of many conifers allows the snow to slide
off their branches so the trees are not crushed by
the weight of the snow.

THREATS TO FORESTS

Many temperate forests have been
cut down to make way for farms and
houses. Conifers from other
countries are often planted in place
of broadleaved forests. These
conifers grow faster and their straight
trunks are easier to saw into planks
for timber. But the wildlife is often
unable to live on the new trees.

Spruce and
larch plantations
in Scotland

Grey squirrels
(Sciurus
carolinensis)
bury acorns to eat
in winter. They do not
find them all so some
acorns sprout into new trees.

Centipedes (Lithobius
forficatus) live in
damp places such
as leaf litter. They
come out at night to
hunt for food such
as spiders, worms,
and woodlice.

Find out more

Climates p.244
Conifers p.317
Flowering piants p.318
Transport in piants p.341
Cycles in the biosphere p.372
Migration and hibernation
p.381

396

ECOLOGY

TOWNS AND CITIES

pipistrelle bat
(Pipistrellus
pipistrellus)
roosts in roofs.

Food left out
on bird tables
helps birds -
and squirrels -
to survive
through the
winter.

As THE HUMAN POPULATION GROWS towards
6,000 million, more and more of the Earth’s surface is
taken over by towns and cities. The original wildlife of
the areas now covered by buildings has been driven
out, but some animals and plants have managed to
take advantage of the new shelters. The edible rubbish
we throw away is a major source of food for animals,
and city climates can protect animals and plants
in cold parts of the world. Temperatures can be
several degrees higher than they are in the
surrounding countryside, and there is less
wind, except round tall buildings.

Life in an urban ecosystem

A house and garden, such as this one in a
British urban ecosystem, provide a variety
of living spaces for plants and animals.
Birds such as starlings roost and nest in
the roof, together with bats and squirrels.
Smaller creatures, such as cockroaches,
ants, beetles, and moths, feed and shelter
behind walls, under floors, and in
cupboards. Mice and rats live in drains
and sewers.

House
(Delichon
urbica) nest
under the eaves
of roofs.

Ivy (Hedera
helix) climbs
up walls. It
clings on
to the stone
or bricks.

Spiders spin webs to
trap insects for

RED FOX
The intelligent red
fox (Vulpes vulpes) has
adapted well to living
in a city. It has a varied
diet and will eat almost
anything it can Find, often
raiding bins for food
thrown out by humans.

POSSUMS

The species of
animals that
live in towns and
cities vary in
different parts of
the world
because of
the different
conditions. The brush-tailed
possum (Trichosurus vulpecula) has
adapted well to urban life in
Australia. In the wild it shelters in
burrows, caves, or tree hollows, but
in towns it has learnt to nest in the
roofs of buildings. Colonies of
possums live in parks and they
sometimes become tame enough
to take food from people’s hands.

Part of a garden can be
made into a sanctuary
for wildlife if left to grow
wild. Long grass, weeds,
compost heaps, and
rotting logs will encourage
wildlife to feed and
shelter there.

Bees
nest in
holes in
walls or in
old flower
pots.

Common toads
(Bufo bufo) hide
under stones
during the day
and come out at
night to eat worms,
snails, and woodlice.

Find out more

Pec

Wast

Climates p.244

•PEE AND PLANET P.

ES AND RECYCLING
3 ARTNERSHPS P.37f
Fact finder p.424

374

p.376

397

ECOLOGY

Wildlife in danger

Hundreds OF MILLIONS OF SPECIES of plants and animals
have become extinct (died out) since life began on Earth. Some
of these have died out due to the natural process of evolution.
But, in the past 300 years, people have speeded up the extinction
process more than 1,000 times by destroying habitats, polluting
the environment, and by hunting and collecting species. It is
difficult to work out exactly how quickly species are becoming
extinct, but one estimate suggests that about 100 species a day,

or one species every quarter of
^ kl an hour, disappear for ever.

There are probably one
million species that are in
danger of dying out
within the next 20 years
unless we act now to save
unnecessary extinction.

unknown

Hunting -
and

collecting

Other
causes,
eg disease

Habitat

destruction

Introduced

animals

REASONS FOR EXTINCTION
We do not know the exact reason for
many animal extinctions. This pie chart
shows that habitat destruction and
animals introduced from one place to
another are two major reasons. Hunting
and collecting are also responsible for
the disappearance of many animals.

Untouched wetlands, such as
swamps and marshes, are
a rich habitat for wildlife,
especially insects, fish,
and birds.

Reasons for wetland
destruction include:
drainage and filling in
for farms, towns, ports,
and factories; pollution;
mining for peat, fuels,
and minerals; cutting
trees for timber.

Scarlet ibis
(Eudocimus
ruber)

Destruction of wetlands

Wetlands are one of the world’s most threatened
ecosystems. More than half have already been
destroyed. Some have disappeared due to natural
causes, such as rises in sea level, drought, and
violent storms. But many more have been destroyed
by people. If they are drained, floods and
insects can be controlled to make it safer m

for people to live nearby. But then the ^ 9

wildlife has nowhere to go.

Puerto

Rico: Malaysia:

34 species 9 species Trinjdad

U.S.A.:

Tobago: 5 S p eC j es

BIRDS AT RISK 8 s P ecies
Mangrove swamps
are a type of wetland on tropical
coasts. Birds are especially at risk from
the destruction of mangrove swamps.
This chart shows the estimated
number of bird species in danger of
exinction in mangrove swamps
around the world today.

Seychelles:
Venezuela: 2 species
3 species

RARE PANDA
The giant panda (Ailuropoda
melanoleuca) lives in the bamboo
forests of southwestern China.
But most of the original bamboo
has been cut down and replaced
with villages and rice Fields. It is
thought that there are now only
300-400 giant pandas left. They
live in small areas of bamboo
forest separated by farmland.

PLANTS AT RISK ^
About a quarter of all the plant species 9
in the world are thought to be 9
threatened. They are in danger from 9
habitat destruction, and many plants are 9
taken from the wild to sell. The ’
endangered silver sword (Argyroxilphrum i
kauense ) from Hawaii, shown here, is
threatened by introduced goats, which eat
it, and by plant collectors.

398

ECOLOGY

Mice can be a pest to
farmers, but they were
not the intended prey
for the cane toad. _—

The Australian sugar
cane harvest is
damaged by pests such
as the cane beetle.

The cane beetle
(Dermolepida
albohirtum) eats
the sugar cane.

Native frogs are
not a pest to
sugar-cane farmers.

The cane toad
eats the cane
beetle and
other insects.

The cane toad eats
mice and other
small rodents.

The cane toad eats
geckos and other
lizards.

GEORGE r

SCHALLER

The research done rr -

by American zoologist

Dr George Schaller
(born 1933) has
helped scientists to “

devise conservation
methods. He studied the
behaviour of many animals in the
wild, including pandas in China,
gorillas and lions in Africa, orang¬
utans in Sarawak, and tigers in India.
His many books include The Deer and
the Tiger and The Year of the Gorilla.

Lizards and geckos help
the farmers by eating insects.

The cane toad
(Bufo marinus) was
introduced into the
food web.

Species

INTRODUCTION
In 1935, a species of toad from
Central and South America was
introduced into Queensland, Australia. It
was thought that the toads would eat
beetles that were destroying the sugar
cane. But the toads ate many other
creatures as well. And because they had no
natural predators, the toads multiplied
into huge populations which are now
_destroying the native Australian wildlife.

There are not enough
predators to eat the cane
toad and control its
population - only the
occasional hungry
snake or bird.

MONK SEAL

Monk seals (Monachus species) are
some of the rarest seals in the
world. There are less than 500
Mediterranean monk seals and
1,500 Hawaiian monk seals left,
and the Caribbean monk seal is
now extinct. Pollution of the sea,
fishing, motorboats, and
aeroplanes have disturbed the
seals and caused them to stop
breeding properly.

ZOOS

For a long time, animals were taken from the
wild to fill zoos. Many of these animals were rare
and, by collecting them, zoos were driving them
closer to extinction. Today, most zoos breed
their animals. Some zoos have bred rare
animals, such as the Arabian oryx, golden lion
tamarin, and red wolf, and then released them

into the wild.

1983 :

318,400

skins

1985 :

109,500

skins

Find out more

Cycles in the biosphere p.372
People and pianet p.374
Wastes and recycling p.376
Food chains and webs p.377
Wetlands p.389
Conservation p.400
Factfinder p.424

CATSKIN TRADE

Many animals are still hunted, often illegally,
for their fur, horns, or tusks. Some people like
to wear the skins of large cats, such as leopards
and tigers, as coats. This chart shows the total
world export of catskins. The amount
decreased considerably during the 1980s, but
many cats are still in danger of extinction.

399

ECOLOGY

Conservation

Heath fritillary (Mellicta athalia) -
pedal needs studied and
reintroduced into
the wild

Koala
[Phascolarctos
^^^cinereus) - hunting
banned and protected in
wildlife parks

Sea otter (Enhydra lutris) -
hunting banned and
protected in reserves

Przewalski r s horse
(Equus przewalskii) - bred in captivity
and reintroduced into the wild

By BANNING HUNTING, protecting habitats, setting up
nature reserves, and reducing pollution, many rare species of
animals and plants can be saved. People are starting to realize how
important it is to save wildlife from extinction. Organizations,
such as the Worldwide Fund for Nature (WWF), and
the International Union for the Conservation of
~ « BL Nature and Natural Resources (IUCN), make

Wk people aware of problems and raise money to
protect species and habitats. The
| wildlife on this page shows some
of the species being saved.

Hawaiian goose
(Branta sandvicensis)
bred in captivity and
reintroduced into
the wild

Red wolf (Canis rufus) -
bred in zoos and
reintroduced into the wild

Grey whale
(Eschrichtius glaucus)
hunting banned

EARTH SUMMIT M
In 1992, there was a conference on the jS
environment in Rio de Janeiro, Brazil.
Representatives from governments of most St

countries in the world discussed what S
should be done to save the planet. A special V
“Tree of Life” was created in Rio to which S
paper “leaves” were attached. Written on the
leaves were things people promised to do and
what they thought governments should do.

WILDLIFE RESERVES
The Yellowstone National Park in the
United States was the world’s first
National Park. Today, there are areas of
countryside all over the world that have
been set aside as wildlife reserves. The
plants and animals are protected, as much
as possible, from human hunters,
collectors, and developers who may want
to build on the land. Some of these
reserves cover thousands of square
kilometres. Others are just a small wood,
or piece of undeveloped land in a city.

■Polar bear

(Thalarctos maritimus) - habitat
protected and hunting controlled

HOW YOU CAN HELP

Everyone can do something
to help conserve wildlife.
You can collect paper, tins,
and bottles for recycling.
This will help reduce the
number of trees cut down,
and mines dug under rare
habitats. You can stop
buying things made from
rare animals and plants,
and try to avoid packaging
that cannot be recycled.

European bison

(Bison bonasus) - protected in

nature reserves in Poland

Recycling

symbol

Arabian oryx
(Oryx leucoryx) -
bred in zoos and
reintroduced into
the wild

New Zealand brush lily
(Xeronema callistemon)
protected on island
reserves

Tiger (Panthera
tigris) - hunting
banned, and
protected in
reserves

Find out more

The biosphere p.370
Cycles in the biosphere p.372
People and pianet p.374
Wastes and recycling p.376 '
Wildlife in danger p.398
Factfinder p.424

f Pere David’s deer
(Elaphurus davidiensis)
- reintroduced into the
wild in China from
± reserves in the West

FACTFINDER SECTION

This section contains charts, tables, and maps full of important
scientific information and statistics. The page numbers in this
mini - index will help you look up the things you need to know.

Binary code 411

Body temperature 423

Chemical names

endings and prefixes 404

Classification charts
animals 421

fungi 420

monerans 420

plants 420

protists 420

Climate charts 417

Collecting gases 404

Constellations 419

Conversion tables 409

Earth facts 414

Electromagnetic spectrum 412
Energy consumption 408

Energy supply 409

Equations

electrical 410

light and sound wave 412

in physics 408

Extinction rates 425

Frequency range 413

Gas laws 404

Geological timescale 414

Gestation periods 422

Identifying gases 404

Igneous rocks 415

Industrial chemicals 406

Laboratory apparatus 405

Lifespans 422

Latitude and longitude 414

Metabolic rate 423

Metamorphic rocks 415

Meteorite records 418

Migration routes

425

Mohs’ hardness scale

415

Morse code

411

Periodic chart

402

Photographic exposures

412

Planet facts

418

Plimsoll line

408

Pollution facts

424

Population facts

424

Radioactive decay rates

403

Raw materials
world distribution

407

producers

407

uses

407

Reactivity series

405

Refractive index

413

Resistors

410

Rock cycle

415

Sedimentary rocks

415

SI units

410

Star facts

418

Sun facts

418

Symbols

electrical and electronic

411

elements

402

410

weather

416

Temperature scales

Celsius

408

fahrenheit

408

Kelvin

408

Units of measurement

409

Vitamins

423

Weather centres

417

Weather records

416

401

FACT FINDER • MATTER

MATTER

PERIODIC CHART

In this chart, the elements are arranged in order of
increasing atomic number, as they are in the traditional
periodic table. The relative atomic mass shown here is for
the most common isotope or, for radioactive elements, the

most stable isotope. Where no data is shown, the element is
so short-lived and has been made in such small amounts
that it has not been possible to discover its properties.

See pp. 22, 24,31,32.

Symbol

8
9

20
21
22

Element

Hydrogen

Helium

Lithium

Beryllium

Boron-

Carbon

graphite

diamond

— Nitrogen

— Oxygen-

— Fluorine-

Neon-

Sodium-

Magnesium

— Aluminium

— Silicon-

Phosphorus -

white —

— Sulphur-

rhombic

— Chlorine-

Argon

— Potassium
Calcium —
Scandium

— Titanium —
Vanadium

— Chromium —
Manganese -

— Iron-

Cobalt —
Nickel

Copper

Zinc

Gallium-

Germanium
Arsenic —

Selenium

Bromine

Krypton

Rubidium

Strontium

Yttrium-

Zirconium

Niobium

Molybdenum
Technetium
Ruthenium
Rhodium
Palladium
Silver

Cadmium-

Indium -

Tin -

Antimony
Tellurium
Iodine
Xenon —

Li —

O-

P -

V-

Relative \

ATOMIC MASS

Melting
°C

- 4 -

-7

11 -
12

-14

20
23

- 24 -

28
31

- 35 -

40
45 -
48 -

56
59
59

65
70

73 -
-75 —
80

79 —

85
88
89

91 —
93

96 -

97 -
101
103
106
108
112
115
119
121
128
127
132

-259

-272

179

1283

2300

none

3500

-210

-219

-220

-249

650

660

1420

44 111

113|

-101

-189

- 848
1541
1677
1917
1903
1244
1539
1495
1455
1083

420

- 30

- 937
none

217

-7

-157

769

1522

1852

2467

2610

2172

2310

1966

1554

-962

321

156

232

631

-450

114

- -112

POINT

°F

-434

-458

354

2341

4170

none

6332

-346

-362

-364

-416

208

1202

1220

2588

235

-150

-308

147

1558

2806

3051

3483

3457

2271

2802

2723

2651

1981

788

1719

none

423

-251

102

1416

2772

3366

4473

4730

3942

4190

3571

2829

1764

610

313

450

1168

842

237

-170

Boiling point
°C °F

Valency

-253

-269

1340

2990

-3660

3640

4827

- -196
-183
-188

- -246
890

1105

2467

2355

280

445

-34

-186

754

1487

2831

3277

3377

2642

2041

2750

2877

2730

2582

907

2403

2355

613

685

-152

688

1384

3338

4377

4742

5560

4877

3900

3727

2970

2212

767

2028

2270

1635

990

184

-107

-423

-452

2440

5400

6620

6580

8721

-321

-297

-306

-410

1634

2021

4473

4271

536

833

-29

-303

1389

2709

5128

5931

6111

4788

3706

4980

5211

4950

4680

1665

4357

4271

1135

1265

138

-242

1270

2523

6040

7911

8568

10040

8,811

7052

6741

5378

4014

1413

3680

4118

2975

1814

363

-161

1 —
2 —
3 —
2,4

3,5

2 -

1 -

4 —
3,5

2 , 4,6

1 , 3 , 5,7

1 --

2 —

3,4

2 , 3 , 4,5
2 , 3,6
2 , 3 , 4 , 6,7
2,3
2,3
2,3
1,2
2

2,3
4 —

3,5
2 , 4,6
1 , 3 , 5,7
0
1
2

3 —

3,5

2 . 3 . 4 . 5.6

2 . 3 . 4 . 6.7
3 , 4 , 6,8

3.4

2.4
1

1.3

2.4

3.5

2 , 4 , 6 —

1 , 3 , 5 , 7 —
0

Date

OF DISCOVERY

T768-=

1868/1895

1817

1798

1808

Physical description

ancient

1885 —
1772

1886
1898
1807 -
1808 -
1825 -
1824
1669

ancient

1774 —
1894

1807

1808 -
1879
1795 -
1801 -
1797
1774 -
ancient
1735 -
1751
ancient
1746 -
1875
1886
1250
1817 -
1826
1898
1861 —
1808
1794 -
1789
1801 -
1778
1937
1844 —
1803
1803
ancient
1817
1863
ancient
ancient
1782
1811
1898

colourless gas
colourless gas
silvery-white metal
grey metal
dark brown powder

black solid
colourless solid
colourless gas
colourless gas
pale green-yellow gas
colourless gas
silvery-white metal
silvery-white metal
silvery metal
dark grey solid

waxy solid

yellow solid
yellow-green gas
colourless gas
silvery-white metal
silvery-white metal
metallic
silvery metal
silvery-grey metal
silvery metal
red-white metal
silvery-white metal
red-white metal
silvery-white metal
pink metal
blue-white metal
grey metal
grey-white metal
steel-grey solid
grey solid
red-brown liquid
colourless gas
silvery-white metal
silvery-white metal
steel-grey metal
-steel-white metal
grey metal
silvery metal
silvery-grey metal
blue-white metal
steel-blue metal
silvery-white metal
shiny white metal
blue-white metal
blue-silvery metal
silvery-white metal
silvery metal
silver-grey solid
purple-black solid
colourless gas

402

FACT FINDER • MATTER

Atomic n

NUMBER/

60
61
62

80
81
82

99
100
101
102

103

104

105

106

107

108
109

Element

Caesium

Barium

Lanthanum

Cerium

Praseodymium

Neodymium

Promethium

Samarium

Europium

Gadolinium

Terbium

Dysprosium

Holmium

Erbium

Thulium

Ytterbium-

Lutetium-

Hafnium

Tantalum

Tungsten

Rhenium

Osmium-

Iridium

Platinum

Gold

Mercury

Thallium

Lead

Bismuth

Polonium

Astatine —

Radon

Francium

Radium-

Actinium
Thorium
Protactinium —
Uranium

Neptunium-

Plutonium

Americium

Curium

Berkelium

Symbol

Californium
Einsteinium
Fermium
Mendelevium
Nobelium
Lawrencium
Unnilquadium
Unnilpentium
Unnilhexium -
— Unnilseptium -
Unniloctium
Unnilennium

Tm -

Fr —

Ra-

Fm-

Md-

Unq

Unp

Unh

Uns

Uno

Une

Relative

v ATOMIC MASS/

Melting
°C

133

137

139

140

- 141 "
142
145
150
152

- 157
159
163

- 165-
167

- 169-

- 173-
175
179

- 181 -
184"

- 186"
190
193
195
197
201
204
207

209

210
211 -
222
223
226

-227-

232

231

238

237

242

-243-

247

251

-254

-253-

-256-

254

257

261

-262-

263

262

265

266

29
725
921
799
931
1021
1168
1077
822
1313
1356
1412
1474
1529
1545
819
1663
2227
2996
3410
3180
3045
2410
1772
1064
-39
303
- 328
271
254
300
-71
27
-700
1050
1750
1597
1132
637
640
994
1340
1050
900
860

POINT

°F

1337

1690

1470

1708

1870

2134

1971

1512

2395

2473

2574

2685

2784

2813

1506

3025

4041

5425

6170

5756

5510

4370

3222

1947

-38

577

622

520

489

572

-96

1292

1922

3182

2907

2070

1179

1184

1821

2444

1922

1652

1580

Boiling point
°C °F

Valency

671
1640
3457
3426
3512
3068
2700
1791
1597
3266
3123
2562
2695
2863
1947
1194
3395
4602
5427
5660
5627
5090
4130
3827
2807
-357
1457
1744
1560
-962
370
--62
677
1200
3200
4787
4027
3818
4090
3230
2607
3190
— 710
1470
996

1240

2984

6255

6199

6354

5554

4892

3256

2907

5911

5653

4644

4883

5185

3537

2181

6143

8316

9801

10220

10161

9190

7466

6921

5080

675

2655

3171

2840

1764

698

-80

1251

2190

5792

8649

7281

6904

7394

5850

4724

5774

1310

2678

1825

— r i-
2

3.4
3

3—

2,3

3 —

2,3

2.3

4 -

3.5

2 , 4 , 5,6

1.4.7

2 , 3 , 4 , 6,8

3.4 -

2.4 -
1,3
1,2

1.3

2.4

3.5
2,3,4

1.3.5.7 —
0

2 —

4 -

— 4,5-

3.4.5.6 —

2.3.4.5.6
2,3,4,5,6
2,3,4,5,6
2,3,4
2,3,4
2,3,4
2,3

2,3
2,3 —

2,3 —

Date

OF DISCOVERY

Physical description

1860

1808

1839

1803
1885

1885
1947

1879
1896

1880
1843

1886
1878-9
1843
1879
1878
1907
1923 -
1802
1783
1925

1804
1804
1735
ancient
ancient
1861
ancient
1450
1898

1940 -

1900

1939

1898

1899
1828
1917 -
1789

1940
1940
1944
1944

1949

1950
1952
1952
1955
1958
1961

1964,1969

1970

1974

1976

1984

1982

silvery-white metal

metallic

dark grey solid

steel-grey metal

yellow-white metal

metallic

light grey metal
steel-grey metal
silvery-white metal
silvery metal
metallic
silvery metal
grey-silver metal
metallic
silvery metal
metallic

steel-grey metal
silvery metal
grey metal
white-grey metal
grey-blue metal
silvery-white metal
blue-white metal
shiny yellow metal
silvery metallic liquid
blue-grey metal
steel-blue metal
red-silvery metal
metallic
metallic
colourless gas
metallic
silvery metal
metallic
grey metal
silvery metal
blue-white metal
silvery metal
silvery metal
silvery-white metal
silvery metal
silvery metal
silvery metal
silvery metal
metallic
metallic
metallic
metallic

RADIOACTIVE HALF LIVES

Radioactive elements decay at different rates. A half-life is the time it takes for half of the original amount of radioactive element to decay. Different
elements emit different types of radiation when they decay - alpha particles (a), beta particles ((3), and always gamma rays (y).

Uranium-238 oc

4,500 million years^

Plutonium-239 00
24,400 years ^

Carbon-14 (g)

5,700 years w

Radium-226 (X)

1,600 years *

Strontium-90 (JJ)

28 years *

Hydrogen-3 (g)

12.3 years *

Cobalt-60 ®

5.3 years (beta w
and gamma rays) ^ W

Phosphorus-32 (g)
14.3 days w

Iodine-131 (g)

8.1 days w

Radon-222 ©

3.8 days w

Lead-214 (g)

26.8 minutes W

Astatine-215 @

0.0001 seconds W

403

FACT FINDER • REACTIONS

REACTIONS

GAS LAWS

The gas laws predict
how a gas will behave
if you change its
conditions - that is, its
temperature (T), its
pressure (P), or its
volume (V). In the
equations below, the
symbol K represents a
constant number.

Temperature

Graham’s Law of Diffusion

If the temperature and pressure are constant, the rate of diffusion of a gas
depends on its density. A high density gives a low rate of diffusion. So gases
with light molecules will diffuse faster than gases with heavy molecules.

Cotton wool clipped White ring of
in ammonia ammonium

chloride

Cotton wool
dipped in
hydrochloric acid

Gas

molecules

Ammonia gas Hydrogen chloride gas

A white ring of ammonium
chloride forms where the
gases meet. Ammonia
molecules are lighter than
hydrogen chloride molecules,
and so they diffuse faster.
This means the white ring
forms nearer to the right-
hand end of the tube.

Boyle’s Law

If the temperature is
constant, the pressure of
a gas is inversely
proportional to the volume
(the gas will contract if the
pressure is raised): PV=K

Pressure Law

If the volume is constant,
the pressure of a gas is
directly proportional to the
temperature (the pressure
increases if the
temperature rises): P/T=K

Charles’ Law

If the pressure is constant,
the volume of a gas is
directly proportional to the
temperature (the gas will
expand if the temperature
is raised): V/T=K

Ideal Gas Law

The ideal gas law combines Boyle’s Law, Charles’ Law, and the Pressure
Law into one equation. All the gas laws will work best for gases that have
small, widely spaced molecules - gases that are said to behave like an
ideal gas. (R is the gas constant. It is the same for all gases.)

PV=RT

Avogadro’s Law

At the same temperature and pressure, equal volumes of
all gases contain the same number of molecules.

Two volumes
of carbon
dioxide

Two volumes ^
of carbon
monoxide

O O
O O

o o ...

o o

Two volumes of carbon monoxide gas would contain exactly the
same number of molecules as two volumes of carbon dioxide
gas (even though carbon dioxide molecules are much heavier).

Gay-Lussac’s Law

If the temperature and pressure are constant, when gases
react to produce other gases, the volumes of the reactants
and the products are in a ratio of simple whole numbers.

200(g)

°2<g>

2C0 2 (g)

400 cm 3

200cm 3

400cm 3

Two volumes of carbon monoxide gas will always react with one
volume of oxygen gas to produce two volumes of carbon
dioxide gas.

COLLECTING A GAS

If a gas is a product of a reaction, it is not easy
to collect it. The set-up of apparatus below
shows how it can be done.

Gas jar
Collected gas

Bung

Reactants

Gas bubbles

Trough
• f water

ENDINGS AND PREFIXES

A chemical name can tell us about the elements the chemical
contains. One way of obtaining this information is by looking at
the endings and the prefixes in a name.

Bunsen burner

Beehive shelf

Compound

Example

To make carbon dioxide gas, for example, the reacting chemicals
would be marble chips (calcium carbonate) and dilute hydrochloric acid.

IDENTIFYING A GAS

Description

-ide

Contains just the two

Iron sulphide

elements in the name.

FeS

-ite

Contains oxygen as well

Iron sulphite

as the other elements in
the name.

FeS0 3

-ate

Contains oxygen as well

Iron sulphate

as the other elements in
the name. Contains more
oxygen than is found in

FeSC >4

-ites.

Carbon dioxide

If you bubble a gas
through limewater
(calcium hydroxide
solution), and the
limewater turns
cloudy, it proves
the gas is g^rbon
dip.

Hydrogen

If you put a lighted
splint into a small
sample of a gas,
and the gas ignites
with a “pop”, it
proves the gas is
hydrogen.

Oxygen

If you put a
glowing splint into
a small sample of
a gas and the
splint relights, it
proves the
gas is oxygen.

Prefix

Mono-

Di-

Tri-

Number of atoms in prefix

Example

Carbon monoxide CO

Dinitrogen oxide
(Nitrous oxide) N 2 O
Nitrogen dioxide NO 2

Boron trichloride BCI 3

404

FACT FINDER • REACTIONS

REACTIVITY SERIES

This is a series that compares the reactivity of different metals. Those at the top are the
most reactive; those at the bottom are the least reactive.

Increasing

reactivity

Metal

Potassium

Sodium

Calcium

Magnesium

Aluminium

Zinc

Iron

Lead

Copper

Silver

Gold

Reaction when heated in air

Reaction with water

Burn vigorously
to form oxides.

Burn with decreasing
vigour down the series.

React slowly to form
oxide layer on surface.

No reaction.

React with cold water to
form hydrogen gas and
alkaline hydroxide
solution. React with
decreasing vigour down
the series.

Do not react with cold
water. React with steam
to form hydrogen gas
and oxide, with
decreasing vigour down
the series.

No reaction.

Reaction with dilute acid

Violent reaction to give
hydrogen gas and salt
solution.

React to form hydrogen
gas and salt solution with
decreasing vigour down
the series.

No reaction.

Increasing
power of
displacement

APPARATUS

Here are some of
the most common
pieces of chemical
equipment used in a
laboratory.

Separating funnel: this
separates two liquids that
do not mix. The denser
liquid settles at the bottom
and can be tapped off first.

Clamp:

this stand
holds
apparatus
in place.

Flat-bottomed flask: this is used for liquid
reactions when no heating is required.

Boiling tube: this tube is made
of thick, heat-resistant glass / ^~

and is used to hold liquids or . C
solids for strong heating. V_

Evaporating dish: this is
used to hold a solution which
is being heated gently to
drive off the solvent.

Pipette: this
is used to
measure
precise
volumes of
liquid.

Test tube: this is used
for chemical reactions on
a small scale. It is not
suitable for strong heating.

/ \

Burette: this is used to
add one solution to
another. It accurately
records the amount of
solution used.

Watch glass: this
is used to hold
solids and to
evaporate small
amounts of liquid.

Volumetric flask: this is used
to make a solution with a very
accurate concentration. The
stopper allows solutions to be
mixed thoroughly.

Beaker: this
is used to
hold a liquid .

Measuring cylinder:

this is used to give
an approximate
measure of the < ^ == 3 S '>
volume of a liquid. \ V

Conical flask: this is used
to carry out reactions.
Unlike the beaker, the flask
can be stoppered.

Dropping pipette: this is used
to add small, but not very
accurate, amounts of one
solutiocLto another ....

tiO^^cH^T^

405

FACT FINDER • MATERIALS

MATERIALS

ALKANES AND ALKENES

Alkanes and alkenes are chemical compounds of hydrogen
and carbon. Although their hydrogen and carbon atoms
are arranged in a similar way, alkanes have only a sipgle
bond between the carbon atoms, whereas alkenes have a
double bond. This difference means that alkenes react
with more substances than alkanes do (see Uses of Ethene,
right). Alkanes are used mainly as fuels. The properties of
alkanes and alkenes change according to the number of
carbon atoms they contain.

USES OF ETHENE

The chemical ethene is obtained during the refining of
petroleum, or crude oil, by a process known as cracking.
This process is carried out in huge chemical plants, where
heat is used to break, or crack, a mixture of hydrocarbons
known as naphtha. By-products are then used for fuel, or as
important raw materials for use in other chemical processes.
Ethene is used on its own to ripen fruit artificially, but when
reacted with the chemicals below, it forms new materials
which have hundreds of uses in the manufacturing industry.

ALKANES

Carbon atoms
in chain

Physical state

ite\

FIX'

Ethene

Name

formula /

methane

gas

ch 4

ethane

gas

c 2 h 6

propane

gas

c 3 h 8

butane

gas

c 4 h 10

pentane

liquid

c 5 h 12

hexane

liquid

c 6 h 14

heptane

liquid

c 7 h 16

octane

liquid

c 8 h 18

nonane

liquid

C 9 h 2o

decane

liquid

C\J

Ethene

Water

Ethene

Benzene

Polyethene

Packaging (cling film, carrier bags,
bottles); moulded articles (buckets,
beakers, kitchenware); other (pipes,
insulating cables, clothing,
photographic film)

Ethanol

Solvent for after-shave lotions,
perfumes, and cosmetics; methylated
spirits; solvent for paints, resins,
soaps, and dyes; other (plastics,
drugs - such as anaesthetics, textiles)

Polystyrene

Ceiling tiles, cavity wall insulation,
cups, bowls, packaging (yogurt pots);
nylon (clothes, carpets, tennis racket
strings, fishing nets); other (car tyres,
latex paints, computer disks, toys)

PVC

Insulating material and protective
covering (gas and water pipes,
hosepipes, insulating cables, roof
fittings, window frames, floor tiles);
wallpaper, curtains, furniture upholstery,
car interior trim, rainwear, protective
clothing, shoes, handbags; chemicals
(fumigant, degreaser), refrigerant; other
(toys, records, recording tape)

Ethane is an example of an alkane
containing a single bond between its
carbon atoms.

ALKENES

Ethene is a typical alkene
containing a double bond between
its carbon atoms.

SODIUM CARBONATE

This important industrial chemical, also known as soda
ash (Na 2 CO 3 ), is made from limestone and salt. Its
major use is in the production of glass. To make glass,
soda ash is heated together with limestone and sand.
Glass is not expensive to produce because there is an
abundance of these raw materials.

Glass

50%

Carbon atoms

/ Carl

in chain

/ Name >

at 22°C (77°F)

/ Molecular

\ /

\ formula

ethene

gas

c 2 h 4

propene

gas

c 3 h 6

butene

gas

c 4 h 8

pentene

liquid

c 5 h 10

hexene

liquid

c 6 h 12

heptene

liquid

c 7 h 14

octene

liquid

c 8 h 16

nonene

liquid

c 9 h 18

decene

liquid

c 10 H 20

Soda ash is mainly used for
glass, chemicals, and
detergents. A small amount
is put to other uses.

Chemicals

25%

Detergents

15%

Other

10%

406

FACT FINDER • MATERIALS

WORLD DISTRIBUTION OF RAW MATERIALS

This map shows the
location of raw materials
throughout the world. In
100 years or so a map
bearing the same title
may look quite different,
as many experts believe
important minerals and
energy sources, such as oil
and natural gas, may have
been exhausted by this
time. Such resources take
millions of years to form
and once they are used up
they cannot be renewed.

LEADING PRODUCERS OF RAW MATERIALS

Material Top producers World total

USES OF RAW MATERIALS

Raw Materials

Uses

Bauxite

(aluminium oxide)

Aluminium is extracted from bauxite
and used for aircraft, foil wrapping,
cars, paints, and kitchen utensils.

Coal

Coal is mainly made of carbon and is
used as fuel. This fuel is used to heat
homes, and to generate electricity.

Copper

Copper is used to conduct electricity
in wires and cables, and to make a
range of alloys such as brass.

Natural gas

This is used to make ammonia. It is
also used in the home as a fuel for
heating and cooking.

Iron ore

Engine parts for cars are made out of
iron, and so are magnets. Iron is also
used to make steel. Steel is stronger
than iron and is one of the main
materials for building bridges.

Kaolin (clay)

This is used in the manufacture of
bricks to build houses, ceramics to
make pottery, and cement.

Oil

Oil is used to make plastics, and as a
fuel for aeroplanes and cars.

Salt

This is used as a food flavouring, and
to make sodium hydroxide (caustic
soda) and sodium carbonate.

Sulphur

This is used to make sulphuric acid,
which is used to make paints,
detergents, plastics, and fibres.

Wood

Wood is used to make buildings,
beams, doors, and furniture. It is also

the raw material for making paper.

Bauxite

(aluminium oxide)

Australia 41.7 million
Guinea 16.3 million

110 million

Coal

Copper

Natural Gas

Iron ore

Kaolin (clay)

Salt

Sulphur

Wood

All figures in tonnes
Except m 3 = cubic metres

China 1,116 million
U.S.A. 858 million

4,800 million

Chile 2.1 million
U.S.A. 1.79 million

10 million

C.I.S. 796,000 million m 3
U.S.A. 521,000 million m 3

2 , 100,000

million m 3

C.I.S. 241 million
China 234 million

1,000 million

C.I.S. 2 million
Republic of Korea
1.3 million

23.1 million

C.I.S. 607 million
U.S.A. 373 million
Saudi Arabia 257 million

2,987 million

U.S.A. 38 million
China 29.5 million

190 million

U.S.A. 38 million
China 29.5 million

190 million

U.S.A. 1,109 million m 3
C.I.S. 862 million m 3

7,147 million
m3

407

FACT FINDER • FORCES AND ENERGY

FORCES AND ENERGY

EQUATIONS

The following equations are commonly used in
physics. Some of the units used to calculate these
equations can be found in the metric and imperial
measurement table opposite.

Average speed (m/s)

distance moved (m)
time taken (s)

Force (kgm/s* or N) mass < k 9> x acceleration (m/s*)

Acceleration

ion (m/s 2 )

change in velocity (m/s)
time taken for this change (s)

Momentum (kgm/s) mass ( k 9) x velocity (m/s)

Impulse (Ns)

force(N) x time (s)

Work done (Nm or J)

force (N) x distance moved in the
direction of the force (m)

-work done (Nm) energy change (J)

Average power (J/s or W)^ time taken (s) ° r time taken (s)

Efficiency (%)

work output (Nm) x 100%
work input (Nm)

Pressure (N/m 2 )

force (N)
area (m 2 )

Density (kg/m 3 )

mass (kg)
volume (m 3 )

Key:

J - joule kg - kilogram m - metre N - newton s - second W - watt

Water freezes
0°C (32°F)

TEMPERATURE

SCALES

Temperature is measured
using a thermometer. This
measures how hot or cold
an object or person is. The
higher the reading on the
scale, the hotter the object.
Some objects measure
below zero degrees Celsius,
the freezing point of water,
below which the Celsius
reading becomes a
minus figure.

Centre of Sun
14 million°C
(25 million°F)

Celsius

Fahrenheit

Kelvin

100

212

373

194

363

176

353

158

343

140

333

122

323

104

313

303

293

283

273

-10

263

-20

-4

253

AVERAGE DAILY USE OF
ENERGY BY A PERSON

This chart shows how the

energy used by a person
each day can vary
considerably from one
country to the next. The
values include all sources
of energy e.g. food,
electricity, gas
and petrol.

Chile

China 4 million

Australia
16.5 million

Energy used in kJ per 34 million

person per day

United
Kingdom
17.5 million

PLIMSOLL LINE

Ships float because their average
density is less than that of water.
But an overloaded ship will sink.
Every merchant ship has a mark
called the Plimsoll line painted on
its hull. If this line sinks below sea
level, the load is too heavy.

These lines indicate

safe load levels in

Water Of different Tropica l Fresh

temperatures and

saltiness. ^ _ Fresh

Summer

V-’-' -P

Winter

The Plimsoll

408

FACT FINDER • FORCES AND ENERGY

METRIC AND IMPERIAL MEASUREMENT

U NITS OF MEASUREMENT
\ Metric unit

Length

1 centimetre (cm)

1 metre (m)

1 kilometre (km)

Area

1 square centimetre (cm 2 )

1 square metre (m 2 )

1 hectare (ha)

1 square kilometre (km 2 )

Volume

1 cubic centimetre (cc or cm
1 litre (I)

1 cubic metre (m 3 )

Mass

1 kilogram (kg)

1 tonne (t)

Equivalent

10 millimetres (mm)

100 centimetres
1,000 metres

100 square millimetres (mm 2 )
10,000 square centimetres
1,000 square metres
1 million square metres

1 millilitre (ml)

1,000 millilitres
1,000 litres

1,000 grams (g)
1,000 kilograms

Imperial unit

■x

Length

1 foot (ft)

1 yard (yd)

1 mile

Area

1 square foot (ft 2 )

1 square yard (yd 2 )
1 acre

1 square mile

Volume

1 pint
1 quart
1 gallon

Mass

1 pound (lb)

1 ton

Equivalent

12 inches (in)

3 feet

1,760 yards

144 square inches (in 2 )
9 square feet
4,840 square yards
640 acres

34.68 cubic inches (in 3 )
2 pints

4 quarts

16 ounces (oz)
2,240 pounds

METRIC UNITS INTO IMPERIAL UNITS

IMPERIAL UNITS INTO METRIC UNITS

To convert

Multiply by f

To convert ?

Into

s. Multiply by

Length

centimetres

inches

0.39

inches

centimetres

2.54

metres

feet

3.28

feet

metres

0.30

kilometres

miles

0.62

miles

kilometres

1.61

Area

square cm

square inches

0.16

square inches

square cm

6.45

square metres

square feet

10.76

square feet

square metres

0.09

hectares

acres

2.47

acres

hectares

0.40

square km

square miles

0.39

square miles

square km

2.59

Volume

cubic cm

cubic inches

0.061

cubic inches

cubic cm

16.39

litres

pints (imperial)

1.76

pints (imperial)

litres

0.57

litres

gallons (imperial)

0.22

gallons (imperial)

litres

4.55

Mass

grams

ounces

0.04

ounces

grams

28.35

kilograms

pounds

2.20

pounds

kilograms

0.45

tonnes

tons (imperial)

0.98

tons (imperial)

tonnes

1.02

CHANGING ENERGY SUPPLIES

The following diagram
shows how the world’s
energy supply has
changed since 1850.

Using the key below, it
becomes clear that the
increasing sources of
energy are oil, gas, and
nuclear energy.

100 %-

75% _

Power source

Muscles

Wood

Coal

Oil

Gas

Nuclear

50% ■

25%-

0 %-

1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990

A / A /

4 )

409

FACT FINDER • ELECTRICITY AND MAGNETISM

ELECTRICITY AND MAGNETISM

SI UNITS - TABLE OF SYMBOLS

SI units are an internationally agreed system of units used for scientific
purposes. The full official name of this system is Systeme International d’Unites.
Multipliers commonly used with some electrical units include: pico- (symbol p,
x 1/1,000,000,000,000); micro- (symbol p, x 1/1,000,000); milli- (symbol m,
x 1/1,000); kilo- (symbol k, x 1,000); and mega- (symbol M, x 1,000,000).

Quantity

Symbol

Unit

Abbreviation

Explanation

voltage

volt

A battery or generator produces a
voltage that makes current flow in a
circuit. 1 volt will drive a current of

1 amp through a resistance of 1 ohm.

current

ampere
(or amp)

A current is a flow of charged
particles, usually electrons. A flow of

6 million million million electrons
per second is equal to 1 amp.

resistance

ohm

Resistance is the degree to which a
conductor opposes the flow of
current. Resistance causes some
electrical energy to change into heat.

energy

joule

One joule of electrical energy is
used every second when a current
of 1 amp flows through a resistance
of 1 ohm.

power

watt

Power is the rate at which work is
done or energy is used. A power of

1 watt is equal to a rate of 1 joule
per second.

charge

coulomb

A current is a flow of charged
particles, usually electrons. A
coulomb is the charge moved in

1 second by a current of 1 amp.

EQUATIONS

The expressions shown below are
themselves meaningless, but each
one will enable you to obtain
three equations. Each equation
will show you how to find one of
the three quantities if the other
two are known. All quantities
must be expressed in units of the
same system (such as SI) in order
to obtain the correct answer.

For all the following
expressions, cover the
quantity you want to find.
This gives you:
a = be; b = a_ ; c = a_
c b

electric charge

electric current x time

voltage

current x resistance

power

(dissipated in resistance)

voltage x current

energy

power x time

velocity of waves

frequency x wavelength

b c

RESISTORS

Resistors are used to control the flow of current in a circuit. Resistance is
measured in ohms (Q). The value of a resistor in ohms is usually shown by three
coloured bands on the resistor which are part of a special colour code.

BANDS

Some resistors also have 4th and 5th bands:
- 4 Tolerance. This shows how close the
resistance of a resistor is to the value
marked on it. For example, a 100 Q 2%

temperature.

III /98 Q and 102 Q.

[ / / / / 1 c Tpmnprflti irp pnpffipipnt in nprtQ/millinn

by which the first two
numbers must be

I III/ f w 1 Ull l[Jul dlUl c LUUI1IUIUI 11 III [JcU lo/1II111IUI 1

III (PP m ) P er degree Celsius. This shows

AVV V l q) how much the resistance will change with

multiplied (i.e: how
many zeros to add

in ~ .i

RESISTOR VALUES

The first three bands
are parts of the colour
code (shown below).
The first two stripes
give you the first two
numbers of the
resistor’s value in
ohms. The third stripe
indicates the amount

2 ,200,000 ohms
(or 2.2 M Q)

24,000 ohms

CODE

Brown

Red

Orange

Yellow

Green

Blue

Violet

Grey

White

Gold

Silver

Band 1

1st fig.

Band 2
2nd fig.

Band 3
multiplier

100

1,000

10,000

100,000

1 million

10 million

0.1

0.01

Band 4
tolerance

1 %

2 %

0.5%

0.25%

0 .1%

10 %

Band 5

temp.

coefficient

200

ppm/°C

100

ppm/°C

7,500 ohms
(or 7.5 k Q)

650 ohms

ill

35 ohms

70 ohms

410

FACT FINDER • ELECTRICITY AND MAGNETISM

ELECTRICAL AND
ELECTRONIC SYMBOLS

Commonly used symbols for some
components found in electrical and
electronic circuits are shown below.
Alternative symbols are sometimes used for
many components, especially in books
published in other countries.

MORSE CODE

Messages can be sent in Morse code as combinations of short and long
signals called dots and dashes. These signals represent letters, numbers,
and other characters.

• —

—

— •-

— • • •

— •

-• •

•

—

•-

— • •

•

• •-

•

-• —

• • •-

• • — •

• — •

• • • • —

-•

• • •

• • • •

—

— • • • •

• •

• • —

-• • •

•-

• • • —

-• •

— • —

•-

-•

• — • •

— • • —

BINARY CODE

Electronic calculators use the binary system of numbers. This has
just two digits, 0 and 1, unlike the decimal system, which has ten
digits, from 0 to 9. In the decimal system, long numbers represent
(from right to left) units, tens, hundreds, thousands, and so on.

In the binary system, long numbers represent units, twos, fours,
eights, and so on.

Binary numbers Decimal numbers

(•)

( 2 )

(10)

(0)

(»)

(0)

(o)

( 2 )

(0)

(o)

( 2 )

(°)

(»)

( 4 )

(0)

(o)

( 5 )

( 0 )

CjJ

(0)

( 7 )

(0)

( 0 )

(0)

(1)

(0)

( 9 )

(0)

(°)

(0)

(_L)

(o)

(3)

C 1 )

(0)

(4)

( 1 )

( 5 )

411

FACT FINDER • SOUND AND LIGHT

SOUND AND LIGHT

WAVE EQUATION

The amplitude of the wave (a) is the height of
a crest (or trough) from the zero line. The
distance between one crest and its
neighbouring crest is known as the wavelength
(^). The number of waves produced every
second is called the frequency (/).

Low frequency

High frequency

Long wavelength

Short wavelength

The formula for any wave

wave speed = frequency x wavelength

(m/s) (Hz) (m)

PHOTOGRAPHIC EXPOSURES

Exposure is a combination of shutter speed and
aperture. This diagram shows how, by keeping a
constant shutter speed of 1/250 with a 200ASA
film, the aperture can be changed to achieve the
correct exposure for the different lighting
conditions shown.

Bright sunshine

Correct exposure

Subject in shade

f5.6

Correct exposure

THE ELECTROMAGNETIC SPECTRUM

The light that we see is one type of electromagnetic radiation.
There are many others as shown below. These waves all travel
at the same speed but differ in their wavelength.

Wavelength

(metres)

-10

—10

— 10

-10' 6

- 10 "

-10‘ 8

- 10 1

10 1

■e

Type of
radiation

Detectable

objects

0 )

'•5

House

Cabbage

Atom

Nucleus

Proton

< 8 >

Quarks

TV transmits

Ultraviolet lamp

Nuclear explosion

412

FACT FINDER • SOUND AND LIGHT

REFRACTIVE INDEX

The speed change when light travels from one
transparent material to another causes it to change
direction. The greater the change in speed, the
more the light bends.

The refractive index is the ratio between the speed at
which light travels in a vacuum and the speed it
travels in another substance.

Angle i = angle of incidence
Angle r = angle of refraction

Incident

ray

Refractive index
of a substance

Speed of light in a vacuum
Speed of light in substance

The refractive index of water (1.33) is less than that
of glass (1.5). This means that the light is slowed
down more and so is bent more when it passes
through glass, than when it passes through water.

Substance

Refractive

index

Speed of light
(m/s)

Air

1.0

300,000,000

Water

1.33

225,000,000

Perspex

1.5

200,000,000

Glass

1.5

200,000,000

Diamond

2.4

120,000,000

Angle of refraction

The angles shown in the above
diagram can also be used to
measure refractive index, from
another formula called Snell’s Law.

Snell's Law

Refractive

Sin i

index

Sin r

FREQUENCY RANGE OF MUSICAL INSTRUMENTS

All instruments produce a sound by making something
vibrate. The vibrations produce soundwaves in the air.

These waves travel to our ears and produce rapid changes
in air pressure at the same rate as

Tuning fork

This produces a pure note of one
frequency. Other instruments
usually produce many

frequencies at the same time
to give a complicated
waveform.

Flute

The pure fluid sound of the
flute is reflected in the smooth
curves of its regular waveform.

Oboe

The rich sounds made by reed
instruments such as the oboe
contain many more frequencies
than the purer sounds of
the flute.

the vibration of the instrument. The sound wave from each
instrument has its own kind of pressure changes, which can
be shown below by curved and jagged lines that are called
waveforms.

AWlWlWiWW\

Clarinet

The single reed of the clarinet
produces a smooth, warm tone.

Violin

The bright sound of the violin
contains many High frequency
harmonics producing a very
jagged waveform.

Cymbal

The crashing sound of the
cymbal corresponds to a
jagged irregular wave
pattern which rises and falls
in an almost random way.

413

FACT FINDER • EARTH

EARTH

GEOLOGICAL TIMESCALE

The history of Earth is outlined in the geological timescale, and
calculated by studying the ages of the various layers of sedimentary rock.

The figures of “Time began” given here are for millions of years.

LATITUDE AND LONGITUDE

At 0° latitude lies the line of the Equator,
0° longitude runs through Greenwich,
London, England. The positions of
places are calculated by the degrees of

Equator between the Poles

STRUCTURE OF THE EARTH

Depth

(km)

rse—

400

1,000

2,900

5,100

6,360

Pressure Density

(k bar) (kg/m 3 )

0 0

(TOO-

^000

150

3,500

325

4,500

1,325

10,000

3,300

12,100

3,750

12,100

Temperature

(°C)

Mohorovicic

Discontinuity

Gutenberg

Discontinuity

The Earth contains four layers. The outer
layer, the crust, is made of different types of
rocks such as basalt and granite. The mantle
also contains rocks but these are heavier and
darker than those found in the crust. The
outer core is liquid and is thought to contain
liquid iron, sulphur, and silicon. The inner
core probably contains solid iron.

Crust

Upper mantle

Transition zone

Mantle

Outer core

Core

414

FACT FINDER • EARTH

MOHS’ SCALE OF HARDNESS

Friedrich Mohs, a German minerologist, created a table of
ten minerals to show their hardness. The higher the
number, the harder the mineral. Each mineral can scratch
those of a lower number.

J2w

6 Orthociase

A fingernail has a
hardness of
about 2.5.

2 Gypsum

7 Quartz

^fll

3 Calcite

8 Topaz

A copper coin has

1 %

a hardness of 5.5.

W *

4 Fluorite

9 Corundum

5 Apatite

10 Diamond

A penknife has a
hardness of 5.5
and can scratch
apatite but not
orthociase.

THE MOST COMMON ROCKS

All the rocks that make up the Earth are igneous,
sedimentary, or metamorphic rocks. Igneous rocks
form when molten rock is cooled. Sedimentary rocks
are fragments of rock, sand, and silt compressed to
form a solid mass. Metamorphic rocks form when heat
and pressure change the mineral content of a rock.

Below are ten common examples of each.

Igneous

Sedimentary

Metamorphic

Granite

Limestone

Slate

Syenite

Dolomite

Phyllite

Gabbro

Sandstone

Schist

Dolerite

Conglomerate

Gneiss

Basalt

Breccia

Hornfels •

Andesite

Evaporite

Marble

Obsidian

Siltstone

Quartzite

Diorite

Mudstone

Migmatite

Porphyry

Shale

Amphibolite

Rhyolite

Clay

Tactite

Sedimentary

rock

THE ROCK CYCLE

The Earth’s crust is made of recycled rocks. These are formed by
external factors such as heat, pressure, and weathering. These factors
are continually breaking up and rebuilding sedimentary, igneous, and
metamorphic rocks in a process known as the rock cycle.

—

Molten rock in the mantle

Extrusive

igneous

rock

Key

Emplacement

—i/ Metamorphism

Solidification

Fusion

Erosion

I—k Uplift

i—Deposition

.—k Lithification
k (rock formation)

—

Intrusive igneous
rock

Metamorphic

rock

415

FACT FINDER • WEATHER

WEATHER

WORLD METEOROLOGICAL ORGANIZATION

The World Meteorological Organization consists of a
network of about 10,000 national weather stations all over
the world. Reports from these stations are sent by
telephone every three hours to the thirteen main weather
centres shown on this world map. This information is
then continually passed around the world to national
weather stations, which put together their own weather
forecasts.

EXTREMES IN WEATHER CONDITIONS

This chart shows the extreme weather conditions recorded around
the world. In some places, extreme conditions are part of the
normal seasonal weather pattern for that area. In others, con¬
ditions such as floods and droughts can interrupt the usual pattern.

Greatest snowfall

(12 months) 31,102 mm (1,224.5 in). Paradise, Mount Rainier,
Washington State, U.S.A. 19/2/1971 to 18/2/1972.

Greatest rainfall

(24 hours) 1,870 mm (73.62 in). Cilaos, Reunion, Indian Ocean.

15/3 to 16/3/1952.

Driest place/longest drought

(Annual average) Nil, in the Atacama Desert, near Calama, Chile.

400 years to 1972.

Highest surface wind speed

371 km/h (231 mph), Mount Washington (alt. 1,916 m/6,288 ft).

3 W Hampshire, U.S.A. 12/4/1934.

Maximum sunshine

97% of daylight hours (over 4,300 hours). Eastern Sahara.

Minimum sunshine

^ Nil, South Pole - for stretches of 182 days in winter.

Highest shade temperature

58°C (136°F). al' Aziz yah, Libya (alt. Ill m/367 ft).

13/9/1922.

Hottest place

(Annual average) 34.4°C/94°F. Dallol, Ethiopia.

Coldest place

(Coldest measured average) -57°C (-70°F).

Plateau Station, Antarctica.

Most rainy days

(Year) up to 350 per year, Mount Wai-ale-ali
(alt. 1,569 m/5,148 ft) Kaunai, Hawaii.

Windiest place

Where gales reach 320 km/h (199 mph). Commonwealth Bay,
George V Coast, Antarctica.

READING WEATHER SYMBOLS

Air pressure: 1018 mb-

Temperature: 7°C (45°F)_

Current weather:
continuous heavy rain

Visibility: 2.5 km
(1.5 miles)

Dew point: 6°C (43°F).

Stratus cloud

Cloud cover complete

Equatorial
Counter Current

This map shows the
location of weather centres
around the world. It also
shows the major climatic
regions and ocean currents
of the world.

WEATHER MAP SYMBOLS

Meteorologists use a list of symbols to
indicate weather and wind speed. The symbols shown are
recognized internationally. Once plotted on weather
maps they provide essential information used in making
weather forecasts. Television weather forecasters use
simplified versions of these symbols.

Cloud base: / Rain in
400 m (1,310 ft) past hour

Wind arrows indicate the
direction from which the
wind is blowing - here, a
moderate north-easterly
wind. The marks (‘feathers’)
on the arrows show the
wind speed. Each whole
mark equals a speed of
19 km/h (12 mph), each
half mark 9.5 km/h (6 mph).

Pressure fallen by 2.7 mb in
last 3 hours

-Mist

-Fog

^ Drizzle

• Rain

• Rain and

9 drizzle

• Rain and
snow

Snow

• Rain shower

• Rain and
snow shower

^ Snow shower

A Hail shower

Thunderstorm

^Warm^ront

^Occluded

Light to strong winds

Calm O b 5 5 S S 8 S 8 O Ga,e

416

FACT FINDEK • WEATHER

CLIMATES OF MAJOR CITIES

These graphs show the average temperature and rainfall statistics for various cities around
the world (the locations of these cities are shown on the world map above).

WEATHER

CENTRES

The location of the
thirteen main weather
centres listed below is
shown on the world map.

D Washington, D.C., U.S.A.
H Bracknell, U.K.
jcj Paris, France
FI Offenbach, Germany
H Prague, Czechoslovakia
Q Moscow, Russia
WM Cairo, Egypt
Q New Delhi, India
FI Beijing, China
EH Tokyo, Japan
EO Melbourne, Australia
m Nairobi, Kenya
m Brasilia, Brazil

Polar

Tundra

Temperate

Desert

Tropical

Mountain

-► Ocean currents

417

FACT FINDER • SPACE

SPACE

THE SUN

By far the brightest star in our
sky is the Sun because of its
closeness to Earth. Even so,
the light leaving it takes 8.3
minutes to reach us; the Sun
we see is 8.3 minutes old.

Mass 1.99x10 M g

Surface temperature 6,000°C

Core temperature 14,000,000°C

Diameter 1,392,000 km

LARGEST METEORITES

Name

Country

Approximate

tonnage

Hoba West

South West Africa

The Abnighito Tent

Greenland

30.4

Bacuberito

Mexico

Mbosi

Tanzania

Agpalik

West Greenland

20.1

Armanty

Outer Mongolia

Chupaderos

Mexico

Willamette

U.S.A.

Campo del Cielo

Argentina

Mundrabilla

Australia

BRIGHTEST STARS

The brightness of a star is measured by its magnitude. The
brighter the star, the lower the magnitude number. The apparent
magnitude of a star is its brightness as seen from Earth. The
absolute magnitude is how much light a star actually gives out.

Name

Sirius

Canopus

Alpha Centauri

Arcturus

Vega

Capella

Rigel

Procyon

Betelgeuse

Achernar

Hadar

Altair

Aldebaran

Acrux

Antares

Spica

Pollux

Fomalhaut

Deneb

Beta Crucis

Regulus

Adhara

THE PLANETS

There are nine planets in the Solar System. They fall
roughly into two groups. Closest to the Sun are four rocky
planets. These are Mercury, Venus, Earth, and Mars.

Farther from the Sun are the gas giants. These are Jupiter,
Saturn, Uranus, and Neptune. Pluto is the odd one out - it
is the smallest planet and is made of rock and ice.

Planet

Mercury

Venus

Earth

Mars

K \

Saturn ^

-CiJanus

Neptune

Pluto

Distance from Sun

57.9

108.2

149.6

227.9

778.3

1,427

2,870

4,497

5,913

millions of km (miles)

(36.0)

(67.2)

(93)

(141.5)

(483.3)

( 886 . 1 )

(1,782)

(2,774)

(3,672)

Diameter at equator

4,879

12,104

12,756

6,786

142,984

120,536

51,118

49,528

2,284

km (miles)

(3,033)

(7,523)

(7,928)

(4,222)

(88,784)

(74,914)

(31,770)

(30,757)

(1,419)

Mass (Earth =1)

0.056

0.82

0.107

318

14.5

0.002

Volume (Earth =1)

0.056

0.86

0.15

1,319

744

0.01

Surface temperature °C

-180 to +430

+480

-70 to +55

-120 to+25

-150

-180

-214

-220

-230

(°F)

(-356 to+800)

(+896)

(-158 to+133)

(-248 to+77)

(-238)

(-292)

(-353)

(-364)

(-382)

Surface gravity (Earth=1)

0.38

0.9

0.38

2.64

0.925

0.79

1.12

0.05

Time to orbit Sun (“year”)

87.97 days

224.7 days

365.26 days

686.98 days

11.86 years

29.46 yrs

84.01 yrs

164.8 yrs

248.5 yrs

Time to turn 360° (“day”)

58.65 days

243.01 days

23 h 56 m 4 s

24 h 37 m 23 s

9 h 55 m 30 s

10 h 39 m

17h 14 m

16 h 7 m

6 days 9 h

Orbital velocity km/s

47.9

29.8

24.1

13.1

9.6

6.8

5.4

4.7

(miles/s)

(29.7)

( 21 . 8 )

(18.5)

(15)

( 8 . 1 )

( 6 )

(4.2)

(3.4)

(2.9)

Number of moons

418

FACT FINDER • SPACE

Northern

Hemisphere

CONSTELLATIONS

^ Earth’s sky contains around 6,000 stars that are visible
to the naked eye. The stars that you see depend on
where you are standing on Earth and what time of
year it is. These star maps show the stars that are
I visible from the Northern and Southern
gBngP hemispheres. As the Earth spins, the stars

||v appear to move across the sky and so these
i?.;, maps will need to be rotated too. The stars
in the centre of the maps can be seen all
Wk year round; those at the edge may only
Orion be seen at certain times of the year.

Cetus

Andromeda

Delphinus

Triangulum

Cygnus

Ursa Major

Also known as the
Great Bear. Greek
legend has it that a
beautiful woman
was turned into a
bear by a jealous
goddess.

Cepheus

Monoceros

Polaris
(North Star)

Ursa

Minor

Hercules

Ophiuchus

Draco

Gemini

Canis

Minor

Corona Borealis

Pegasus

This constellation takes the
form of a winged horse. In
Greek legend, the horse
sprang from the blood of a
monster called Medusa, after
it was killed by Perseus.

Cancer

Leo Minor

Bootes Canes
Venatici

Orion

This is one of the
easiest

constellations to
find in the sky. In
Greek legend,
Orion was a
successful but
arrogant hunter.

Southern

Hemisphere

Cetus

Aquarius

Sculptor

Piscis

Austrinus

Canis Major

This constellation
represents one of the two
dogs that are snapping at
Orion’s heels. One of the
stars that makes up Canis
Major is Sirius, the
brightest star in the sky.

Fornax

Capricornus

Phoenix

Microscopium

Eridanus

Tucana

Sagittarius

lorologium
, Reticulum

Hydrus

Caelum

Pavo Corona
Australis

Centaurus

The constellation of
Centaurus shows
the centaur - half
man and half
horse. It contains '
the nearest star
(apart form the
Sun) to Earth -
Proxima Centauri.

Columba

Mensa

Pictor

Canis

Major

Chameleon Triangulum
Australe

Norma

Volans

Carina

Ophiuchus

Scorpiut

Monoceros

Puppis

Centaurus

Scorpius

In Greek legend, this
scorpion was sent to kill
Orion. The characters are
now at opposite ends of the
sky. As Orion sets, the
scorpion rises.

Antlia

Corvus

Crater

419

FACT FINDER • LIVING THINGS

LIVING THINGS

This chart shows how biologists classify the different forms of life
on Earth. It is divided into five major groups, called kingdoms, and
the kingdoms are themselves broken down into several smaller
units. Each organism in the chart contains two pieces of information
about it. First, you will be able to discover which group of the living
world it belongs to. Second, you will be able to see what other living
things are most closely related to it through the process of evolution.

MONERANS

This kingdom includes bacteria,
which are the simplest forms of
life on Earth. There are
over 4,000 species.

FUNGI

Fungi absorb food made by plants
or animals. There are over 100,000
species, classified into

Bacteria

True fungi

100,000 ^

PROTISTS

This kingdom contains simple organisms that mostly have a
single cell. There are at least 65,000 species and most live in
water. A selection of phyla are shown here.

Slime

moulds

10,000

Ciliates

8,000

Brown

Phaeophyta

2,000

Non-vascular

Green algae

Chlorophyta

6,000

Non-vascular

Amoebas

10,000

HOW TO USE THE CHART

The chart is colour-coded so that you can quickly tell the
classification level of any group shown.

Kingdom

Phylum

Subphylum

. The largest grouping in the
classification of living things.

A major group within a kingdom. This
is sometimes called a division when
used in the classification of plants.

Class

. Part of a phylum, or
division, in the
classification of plants.

Subclass

Order

A major part of .
a phylum or
subphylum.

Part of a class or
subclass. Some
classes are split into
many orders.

A large collection of species that
have several features in common.

A small collection of species that
have many features in common.

- A large group
within a class.

Green algae

Chlorophyta _

6,000
Non-vascular

_ Scientific name
. Number of species
_ Further information

A group of living
things that can breed
together in nature.

-pvy a -v The plant kingdom contains organisms that

± 1 j/ \ F\ ^ produce their food using sunlight, together
with some species that have since lost this
ability. The kingdom contains more than 400,000 species. Plants

cannot move, but they reproduce by making spores or seeds.
These often spread far from the parent plant. The simplest plants
reproduce by making spores. The most advanced plants, which
include conifers and flowering plants, reproduce by making seeds.

NON-FLOWERING PLANTS This category includes simple, substances in special vessels. Unlike non-vascular plants, these can live

non-vascular plants, which do not have transport systems for water, salts, in dry places. Some biologists classify algae as non-flowering plants, and

or food. It also includes some vascular plants, which transport these not as protists.

Ferns

Pteridophyta
12,000 ^
Vascular

Club mosses

Lycopodiophyta
400 Vascular

Horsetails

Sphenophyta

550

Vascular

Conifers

Coniferophyta

550

Vascular

Mosses and liverworts

Bryophyta v

25,000 \ ] v

Non-vascular V

FLOWERING PLANTS There are more than 250,000 species of
flowering plant. They are all vascular, and all produce seeds. Flowering
plants such as buttercups have flowers made of many separate parts

arranged symmetrically around the flower stem. Advanced flowering
plants such as foxgloves have fewer parts. These are often fused
together to form funnels or tubes, and the flower shape is often irregular.

Monocotyledons

Plants whose seeds have one cotyledon
(seed-leaf), and leaves with parallel
veins. Flower parts usually in threes,
or multiples of three. Rarely woody.

Dicotyledons

Plants whose seeds have two cotyledons (seed-leaves), and leaves with a branching network of
veins. Flower parts usually in fours or fives, or multiples of these numbers. Many species have
woody stems. There are over 250 families of “dicots”. Some of the most important are shown here.

Elms

Ulmacaeae

140 J*k

Grasses

Graminae

8,000

Irises

Iridaceae 1,850''

Oaks 9

Fagaceae C
-1,050. i\

Heathers

Ericaceae
3,350 A

Foxgloves

Scrophulariaceae

4,500

Orchids

Orchidacei

17,500

Parsley and

Cabbages

carrots

Cruciferae 3,000

Umbelliferae

3,100 ^

JSlIiL

Legumes

Daisies

Leguminosae ,

Compositae, '4§P^

i8.4oo Jm.

420

FACT FINDER • LIVING THINGS

ANIMALS

The animal kingdom contains organisms
that feed on plants, on other animals, or on

their remains. Most animals can move about, but some spend their
adult lives in one place. There may be about 10 to 20 million species.

INVERTEBRATES This informal category contains all animals that
do not have a backbone, and it includes over nine-tenths of all animal

Cnidarians

Cnidaria

9,500

Mainly marine

Corals
Jellyfish
Sea anemones
Hydras

Flatworms

Platyhelminthes

10,000

Free-living flatworms
Flukes
Tapeworms

Molluscs

Mollusca

90,000

Aquatic and terrestrial

Chitons

Slugs and snails
Clams, scallops
Tusks or tooth shells
Octopuses, squids, and
cuttlefish

species. Many invertebrates are soft-bodied and live in water, or in damp
habitats. One phylum, the arthropods, has been outstandingly successful

in water and ah land.

Annelid worms

Annelida

12,000

Aquatic and terrestrial

Earthworms and
bloodworms
Leeches
Lungworms and
other marine worms

Echinoderms
Echinodermata
6,000
Marine
Brittle stars
Sea urchins
Sea cucumbers
Starfish
Sea lilies and
feather stars jm

LaiL

Small phyla

Ctenopora, Rotifera,

Nemertea

3,000+

Comb jellies

Rotifers

Nemertean worms

F/t f

Sponges .. L f yJ\. I

Porifera ’ VVl

- mV

Mainly marine

Nematode worms

Nematoda

12,000

Bryozoans

Bryozoa

4,000

Mainly marine- 5

Arthropods (Arthropods) This large phylum contains animals with a jointed body that is covered by an external skeleton, and divided into a
number of segments. The skeleton supports and protects the body and, on land, it helps to prevent it from drying out.

Crustaceans
; Crustacea
j 40,000
Mainly marine

Water fleas
Wood lice
Crabs and lobsters
Fish lice
Barnacles

Arachnids

Arachnida

70,000

; Mainly terrestrial

Scorpions

Spiders

Mites

Harvestmen

Insects

Insecta 1,000,000+

Springtails

Silverfish and bristletails
Dragonflies and damselflies
Butterflies and moths
Grasshoppers and crickets
Earwigs
Stick insects
Cockroache
Mantids
Termites

Mainly terrestrial

Lice ;

True bugs ^

Thrips
Lacewings
Beetles
Flies
Fleas

Bees, wasps and ants

CHORDATES (Chordata) This phylum contains animals that have a
stiff cord which runs down their bodies. There are about 44,000 species,

and almost all are vertebrates (animals with backbones). The lancelets
and sea squirts, two subphyla, have a stiff cord but not a true backbone.

Jawless fish

Agnatha

Marine; skeleton
made of cartilage

Cartilaginous fish

Chondrichthyes

700

; Marine; skeleton
; made of cartilage

Amphibians

Amphibia

4,000

; Freshwater or terrestrial

Frogs and toads
Newts and salamanders
Caecilians (Apodans)

Bony fish

Osteichthyes

21,000

Marine and freshwater;
skeleton made of bone

Coelacanth

Lungfish

Birchirs

Sturgeons, paddlefish
Eels

Herrings, anchovies
Salmon, trout
Carp

Catfishes
Perches, marlins,
swordfishes, tunas
Angierfish
Cods

Flying fishes
Grunions
Sticklebacks
Seahorses

Reptiles

Reptilia 6,500 Mainly terrestrial;

skin covered with scales

Snakes and lizards
Turtles and tortoises
Crocodiles, alligators^

Tuatara

Birds

Aves 9,000 All breed on land; skin
covetedjn feathers

Divers
Grebes

Albatrosses, petrels
Penguins

Pelicans, gannets, cormorants
Herons, storks
Ducks, geese, swans
Eagles, hawks, vultures
Pheasants, partridges
Gulls, plovers
Pigeons, doves
Parrots

Cuckoos, roadrunners
Owls

Hummingbirds

Kingfishers, bee-eaters, rollers
Perching birds (e.g. finches)

Mammals Mammalia 4,000 Suckle young on milk

Marsupials

Marsupialia

250

Mammals that raise their
young in a poucl

Opossums
Koalas
Bandicoots
Kangaroos

Placentals

Eutheria
3,810

Mammals that nourish their
young through a placenta

Hedgehogs, shrews, moles
Bats

Rabbits, hares

Lemers, monkeys, apes, humai
Anteaters, armadillos
Rodents

Whales, dolphins
Dogs, cats, bears
Seals, sea lions, walruses
Elephants
Hyraxes
Manatees, dugongs
Horses,tapirs, rhinoceroses
Pigs, deer, sheep, antelope, cattle

Monotremes

Montremata

Egg-laying mammals

Duck-billed platypus
Echidnas

421

FACT FINDER • HOW LIVING THINGS WORK

HOW LIVING THINGS WORK

LIFESPANS

Here you can see how long different kinds of organisms
live. With most living things, lifespan is closely linked to
reproduction. Most plants and animals do not surviye for

long after their reproductive life has ended. Bacteria and
protists often reproduce by dividing in two, so their cells
stay alive, even though they have split apart.

10 years

1 month

1 minute

100 years

1,000 years

Bacteria

(Bacterium)

mins

Protists

(Amoeba)

Several days

Fruiting body of ink cap
2-3 days

Hyphae of honey fungus 10 years +

Conifers

Sitka spruce in plantation 10 years + Cedar of Lebanon 500 years

Yew 3,500 years
Bristlecone pine 5,000 years +

Flowering

plants

Saguaro cactus 150 years
m boo-. 30-60 years

Common poppy 6 months

Foxglove 2 years

English oak 1,000 years +

Arthropods

Housefly 17-30 days

Monarch butterfly 1 year

American lobster 50 years

Goldfish 10-25 years
, Whale shark 60 years +
Lake sturgeon 50-80 years

Footprint carp 8 months

Amphibians

Smooth newt 15 years
Fire salamander 20 years

Common toad 40 years

Reptiles

r M Boa constrictor 40 years

* American alligator 60 years

Common lizard 12 years Giant tortoise 150 years

Birds

European robin 1 year Herring gull 25 years

Ostrich 50 years +
Wandering albatross 60 years+

Mammals

Common shrew 1 year

African elephant 75 years 4
Lion 20 years

Red fox 8 years Killer whale 90 years

GESTATION PERIODS

A gestation period is the time between fertilization and birth. In most mammals, it is a precise
length of time. Large mammals usually have long gestation periods, but there are exceptions,
such as the kangaroo, which has a very short gestation period.

15 days — Gestation period

(6-8) -Average number

of young

Golden hamster
15 days (6-8)

Kangaroo
33 days jj&Si

(V FW

Dog • ^
63 days (3-8)

Lion

Virginia opossum
12 days (10-18)

House mouse
20 days (10-14)

110 days (2-3)

Asiatic elephant
660 days

( 1 ) mm

Human
267 days

Goat 1
150 days
(1-2)

Cow I
278 days
( 1 )

Orang-utan \
250 days (1)

Dolphin
360 days (1)

422

FACT FINDER • HOW LIVING THINGS WORK

Human

37°C

Salmon

0°C

30°C

VITAMINS

Vitamins are essential
nutrients that are needed in
very small amounts.

This list shows the daily
vitamin requirements of
an adult.

Vitamins that dissolve in fats

Vitamin A 1 milligram

Vitamin D 7.5 micrograms

Vitamin E 10 milligrams

Vitamin K 100 micrograms

Vitamins that dissolve in water

Vitamin B

Vitamin B 2
Niacin
Vitamin Bg
Vitamin B 12
Pantothenic acid
Folic acid
Biotin
Vitamin C

1.5 milligrams
1.7 milligrams
19 milligrams
2.2 milligrams
3 micrograms
6 milligrams
400 microgram
200 microgram
60 milligrams

BODY TEMPERATURE

“Warm-blooded” and “cold-blooded” are two terms that can be misleading. A desert
pupfish is “cold-blooded”, like all fish. However, it lives in hot springs, so its blood is
actually warm. A “warm-blooded” hibernating bat has a much colder body temperature.

Exothermic (“cold-blooded”) animals

-5°C 0°C 5°C 10°C 15°C 20°C 25°C 30°C 35°C 40°C 45°C

I_I_I_I_L I_I i I

Ice-fish

- 2 °

45°C

Bat

28°

Lizard

18°C

Endothermic (“warm-blooded”) animals

Hedgehog

METABOLIC RATE

Elephant 0.33

Horse 0.52.

Human 1.00

Sheep 1.05

Dog 1.57

Cat 3.24

Rat 4.14

Squirrel 4.90

Shrew 35.24

This chart shows how quickly animals burn their food for each unit of their body weight. The rate for humans is set at one.

House mouse 7.86 —
Harvest mouse 11.90

An animal’s metabolic rate is the rate at which it “burns” its
food to release energy. Here you can see the metabolic
rates of a range of different mammals, compared to that of

humans. Small mammals have to burn their food at a high
rate in relation to their volume; they have a hi gh,su rface
area of skin, through which their bodies 1 —-

423

FACT FINDER • ECOLOGY

ECOLOGY

Growth Rate

This map shows the human
population growth rates in
different parts of the world.

_ Negative: under 0%

_ Low: 0-1%

Moderately low: 1 -2%

□ Moderately high: 2-3%
High: over 3%

POPULATION GROWTH

The world’s human
population has steadily
increased over the years,
and is expected to double
over the next 40 years. This Total 8,448 —
chart shows the increase in
the world’s population, in
millions, through the last
1,000 years and its projected
growth into the twentieth
century. Asia has the
highest population growth.

Total

Asia Oceania 4,082.2

Africa South

America

North and

Central

America

Black Death

A.D. 1000

1975 1990 2025

World

Europe

Total 5,380.5

- 6,000

. 8,000

million

4,000

2,000

POLLUTION

Our wildlife and forests are
damaged by acid rain. This is
caused by the sulphur dioxide
and nitrogen oxides in the fuels
we burn. As they burn, they form
gases that dissolve in water
droplets in moist air. This in
turn falls as rain or snow that
damages the environment.

Key

Commerce
Homes
Industry
Power stations
Rail

Refineries
Road traffic
Others

Sulphur dioxide

424

FACT FINDER • ECOLOGY

Many species of animal are threatened with
extinction, such as those shown below, because
of habitat destruction, pollution, hunting, and
competition from introduced species.

Animal

how rapidly a species becomes
extinct (dies out). A species is
thought to be extinct if it has
not been found in the wild for
the past 50 years. The rate of
extinction has increased over
the past 300 years by human
interference. Some species are
becoming extinct 1,000 times
faster than they did
before people started
to inhabit the Earth.

Number of species
that became extinct
in each year

Balinese tiger
1952

Where found

Numbers

remaining

Tasmanian

wolf/tiger

Asiatic buffalo

Poland

European bison

About 1,000

Passenger
pigeon
^\1914

Mountain gorilla

Rwanda, Africa

Mediterranean monk seal Mediterranean sea

Tarpan

Chinese river dolphin China

China

Giant panda

Whooping crane

North America

Stellar's
sea cow
1768

Great auk
1844

Golden lion tamarin

South America

Assam, India

Dodo

1690

Javan rhino

Java, Indonesia

Kakapo

New Zealand

MIGRATION ROUTES

At certain times of the year, some animals travel from one
area to another. This is known as migration. The average
distances travelled are shown in the box below.

Short-tailed shearwater

32,000 km (19,884 miles)

Golden plover

24,140 km (15,000 miles)

Arctic tern

40,000 km (24,856 miles)

Alaska fur seal

9.600 km (6,000 miles)

Monarch butterfly

5.600 km (3,500 miles)

Whitethroat

2,250 km (1,400 miles)

Wheatear

11,000 km (6,800 miles)

Caribou

2,250 km (1,400 miles)

Blue whale

20,000 km (12,500 miles)

European eel

5,600 km (3,500 miles)

THREATENED SPECIES

RATE OF EXTINCTION

The rate of extinction traces

Words in italic have their own entry
in the glossary.

aa Volcanic lava with a rough surface,
absolute magnitude A measure of the
actual luminosity of a star. (Compare to
apparent magnitude.)

absolute scale A scale of temperature, also
known as the Kelvin scale, that begins at
absolute zero. Its unit of measurement is the
kelvin.

absolute zero The lowest possible
temperature - 0 °K or -273.15 °C
(-459.67 °F)

acceleration The rate of change of velocity.
acid A compound containing hydrogen
which splits up in water to give hydrogen
ions.

acid rain Rain that has become acid due
to water in the air reacting with acids from
power stations and car exhausts. When
acid rain falls it can damage plants and
erode buildings.

acoustics 1. The study of sound. 2. How
sound travels around a room — a concert
hall, for example, must have good
acoustics.

activation energy The energy needed to
start a chemical reaction. A different
amount is needed for every reaction,
adaptation The way in which a plant or
animal changes over many generations to
survive better in a particular environment.
additive Any substance added in small
amounts, especially to food or drink, to
improve it, e.g. to change colour or taste,
adhesion The force of attraction between
the atoms or molecules of two different
substances.

adhesive A sticky substance, such as paste
or glue, used to join two surfaces together.
ADP Adenosine diphosphate. A compound
formed when ATP releases energy,
advection fog or sea fog A type of fog that
forms where warm moist air moves over a
colder surface.

aerobic respiration A type of respiration
that needs oxygen.

aerofoil The special shape of an aircraft
wing - more curved on the top than the
bottom. It produces lift as it moves
through the air.

aestivation The deep sleep or immobility
that some animals go into when the
weather is very hot and dry.
air resistance The force that resists the
movement of an object through the air.
albedo How much an object, especially a
planet or moon, reflects the light that hits
it, i.e. its reflecting power,
alchemy A medieval science that tried,
among other things, to find a way of
changing metals such as lead into gold,
algae (singular alga) Simple plants found
in water. They are non-flowering and do
not have proper stems or roots,
aliphatic compound An organic
compound made up of chains, not rings,
of carbon atoms.

alkali A base that dissolves in water,
alkaline Describes a solution with a pH
greater than 7.

GLOSSARY

allotropes Different forms of the same
element, e.g. diamond and graphite are
allotropes of carbon.

alloy A mixture of two or more metals, or
of a metal and a non-metal,
alternating current (AC) An electric
current whose direction reverses at regular
intervals. (Compare to direct current.)
alternator An electric generator \haX.
produces alternating current.
alveoli (singular alveolus) Tiny air sacs in
the lungs.

AM Amplitude modulation. The
transmission of a signal by changing the
amplitude of the carrier wave,
amalgam An alloy of mercury and another
metal, such as tin.

ammeter An instrument that measures
electric current.

amp (ampere) The unit that measures
electric current.

amplitude The size of a vibration, or the
height of a wave, such as a sound wave,
anabolism A series of chemical reactions in
living things that builds up large molecules
from small ones.

anaerobic respiration A type of respiration
that does not require oxygen. It produces
less energy than aerobic respiration .
analogue Representing a quantity by a
varying electrical voltage. (Compare to
digital.)

andesite Fine-grained brown or greyish
volcanic rock.

angle of incidence The angle a light ray
makes with the perpendicular to the
surface it hits.

angle of reflection The angle a reflected
light ray makes with the perpendicular to
the reflecting surface,
anion A negatively charged ion.
anode A positive electrode.
anodizing The process of coating a metal
object with a thin protective layer of oxide
by electrolysis.

anthracite Hard coal that burns with
hardly any flame or smoke,
antibodies Proteins in the blood which
protect the body by fighting foreign bodies
such as bacteria and viruses,
anticyclone An area of high pressure air
which often produces fine weather,
antioxidant A compound added to foods
and plastics to prevent them oxidizing
and so going stale or breaking down,
antiseptic Able to kill bacteria,
apparent magnitude The brightness of a
star as seen from Earth. (Compare to
absolute magnitude.)

arteries Blood vessels that carry blood
from the heart to other parts of the body.

artificial selection The process by which
humans change the genetic make-up of a
species. (Compare to natural selection.)
asexual reproduction Reproduction that
involves only one parent,
asteroid or minor planet or planetoid. A
rocky body that circles the Sun. Most
asteroids are in the asteroid belt, between
Mars and Jupiter.

asthenosphere A soft layer of the Earth’s
mantle.

astrology The study of how the
movements of the stars and planets may
affect our lives.

astronaut A person trained to be a crew
member in a spacecraft,
astronomy The study of the stars, planets,
and other bodies in space,
atmosphere The layer of gases that
surrounds a planet.

atom The smallest part of an element that
can exist. It consists of a nucleus of protons
and neutrons, surrounded by orbiting
electrons.

atomic number The number of protons in
the nucleus of an atom.

ATP Adenosine triphosphate. A chemical
in plant and animal cells that stores energy,
autoclave A strong, steam-heated
container used for carrying out chemical
reactions and sterilization at high
temperature and pressure,
autotrophic A plant that makes its own
food by photosynthesis.

axis 1 . An imaginary line around which an
object rotates. 2. The line along which
rock bends in a fold.

background radiation 1. Low-intensity
radiation emitted by radioactive substances
in and around the Earth. 2. Radiation (in
the form of microwaves) detected in space
that may have come from the Big Bang.
bacteriophage A parasitic virus that lives
on a bacterium.

bacterium (plural bacteria) A micro-

organism that is a single cell.

barchan (say bar-can) A sand dune with a

crest.

basalt A dark volcanic rock.

base A compound that reacts with an acid

to give water and a salt .

batholith A dome of igneous rock that

solidifies in a huge underground mass.

battery A series of two or more electrical

cells which produce and store electricity.

Beaufort scale A scale used to measure

wind speed, ranging from 0 to 12 (calm to

hurricane force)

Big Bang The theory that the Universe
began with a massive explosion of matter.
It is thought that everything in the
Universe is still moving apart because of
the explosion.

binary system A number system with only
two digits, 0 and 1.
binocular vision The ability of some
animals to see objects in three dimensions
and so judge distance.

426

GLOSSARY

binomial system A system of giving an
organism two names. The first is the genus
and the second the species,
biodegradable A substance that can
decompose and become harmless naturally,
biogas A gas made when plant or animal
waste rots down without the presence of
air.

biogenic Produced by organisms.
biology The study of living things,
biomass 1. The total number of living
organisms in a given area. 2. Plant material
used as a source of energy, e.g. wood that is
burnt to provide heat,
biome A large ecosystem, e.g. a tropical
forest or a desert.

biosphere The region of the Earth and its
atmosphere in which living things are found,
bituminous Containing bitumen, a tar-like
substance produced from petroleum,
black dwarf The faded remains of a dead
star. See also white dwarf.
black hole A highly dense object in space.
Its gravity is so strong that it pulls in
anything around it, even light, so that it
looks black.

black ice Thin, hard, transparent ice,
especially on the surface of a road,
blastocyst A hollow ball of cells.
boiling point The temperature at which a
liquid becomes a gas.

bond The attraction between atoms or ions
which holds them together in a crystal or
molecule.

bone Hard tissue that is part of an
animal’s skeleton.

brine A strong solution of salt in water.
Brownian motion The random movement
of tiny particles in a liquid or a gas, caused
by molecules colliding with them,
buffer 1. A solution that is resistant to
changes in pH. 2. An electric circuit used
to join two other circuits.

CAD Computer-aided design,
caecum (say ky-kum) A pouch in an
animal’s intestines where plant food is
digested.

calorie A unit of energy. The calorie used
in food science is in fact a kilocalorie
= 1,000 calories.

camouflage The colour, markings, or body
shape that helps to hide an animal or plant
in its surroundings.

capacitance The ability to store electric
charge.

capacitor A device used to store electric
charge temporarily.

capillaries Tiny blood vessels which carry
blood to and f rom cells.
capillary action The movement of a liquid
up or down a tube due to attraction
between its molecules and the molecules of
the tube.

carbohydrate An energy-giving compound
made up of carbon, hydrogen, and oxygen,
found in foods such as potatoes,
carbon cycle The circulation of carbon
(contained in carbon dioxide) from the
atmosphere, through plants (by being
trapped in carbohydrates by photosynthesis)
and animals (which eat the plants), and
back into the atmosphere (through
respiration and decomposition).

carnivore A meat-eater,
cartilage Gristly connective tissue which
makes up the soft parts of the skeleton and
is present in some joints. The skeletons of
some fish, e.g. sharks and rays, are made
entirely of cartilage.

cartography The science of map-making,
cast A hollow in a rock, formed around a
since decomposed animal or plant. The
cast is a mould in which minerals collect
and solidify to form a fossil.
catabolism A series of chemical reactions in
living things that breaks down large
molecules into small ones. This releases
energy.

catalyst A chemical that speeds up a
chemical reaction without being changed
itself at the end of the reaction,
catalytic converter A device in a car that
uses a catalyst to change toxic exhaust gases
into less harmful gases,
cathode A negative electrode.
cation A positively charged ion.
cavitation The enlarging of cracks in rock
by compressed air.

celestial body A natural object in space,

such as a planet or star.

celestial pole One of two points in the

celestial sphere about which stars appear to

revolve when seen from Earth.

celestial sphere The imaginary sphere in

which the stars seem to lie when seen from

Earth.

cell 1. The smallest unit of an organism
that can exist on its own. 2. (Voltaic) cell
A device which produces electricity by
chemical change.

cell division The process where one cell
splits to produce two cells, called daughter
cells.

cellulose A carbohydrate that forms the walls
of plant cells.

centrifugal force (or centrifugal effect)

The force that appears to push outwards
on a body moving in a circle,
centrifuge A device used to separate
substances of different densities, by
spinning them round at high speed,
centripetal force The force that pulls
inwards to keep an object moving in a
circle.

Cepheid (say see-fee-id ) star A type of
star that has a cycle of varying brightness,
ceramics Objects made of clay or
porcelain fired in a kiln,
cerebellum The part of the brain at the
back of the skull that controls muscle
movement and balance,
cerebrum The main part of the brain in
the top of the skull that processes
information.

cermet A material made from ceramic and
metal Cermets can withstand very high
temperatures.

CERN Conseil Europeen pour Recherches
Nucleaires. The research centre of the
European Organization for Nuclear
Research in Geneva.

CFC Chlorofluorocarbon. Gases, which if
allowed to escape into the atmosphere, e.g.
from refrigerators and aerosols, will cause
holes in the ozone layer,
chain reaction A reaction which continues
on its own, e.g. a nuclear reaction in which
neutrons from the splitting of one atom go
on to split other atoms.

chemical bond See bond.
chemical Any substance that can change
when joined or mixed with another
substance.

chemistry The study of matter,
chlorophyll The green pigment found in
many plants which absorbs light to provide
the energy for photosynthesis.
chloroplasts Tiny bodies in some plant
cells which contain chlorophyll.
chromatography A method of separating a
mixture by running it through a medium
e.g. filter paper. Different parts of the
mixture move through the medium at
different speeds.

chromosome A structure made up of genes,

which carries the genetic information in a

cell. Chromosomes are arranged in pairs in

the nucleus of a cell.

chromosphere A layer of gases in the

Sun’s atmosphere that shines red.

cilia (singular cilium) Tiny “hairs” on the

surface of many small organisms.

circuit A path around which an electric

current can flow.

climate The normal weather conditions in
an area over a long period of time,
clone Two or more identical organisms that
share exactly the same genes.
cohesion The force of attraction between
two particles of the same substance,
coke A fuel made by baking coal. It is
mostly carbon and gives off much more
heat than coal.

colloid A mixture made up of tiny
particles of one substance dispersed in
another in which it does not dissolve,
colony A large group of the same species
of organism that live together,
coma A cloud of gas and dust that
surrounds the centre of a comet.
combustion (or burning) A chemical
reaction in which a substance combines with
oxygen, producing heat energy,
comet A ball of frozen gas and dust that
travels around the Sun. Some of the dust
streams out from the comet to make a
“tail”.

commensalism Where two or more
organisms live together, and neither causes
harm to the other.

community A group of people or animals
who live in the same place,
commutator A device which reverses the
direction of an electric current,
compound A substance containing atoms
of two or more elements.
compression 1. Being pressed together or
bunched up (e.g. the crest of a sound
wave). 2. The increase in density of a fluid.
concave lens A lens that curves inwards,
concentration A measure of the strength
of a solution, ie the amount of solute
dissolved in a certain amount of solvent.
condensation The change of a gas or
vapour into a liquid,
conduction The movement of heat or
electricity through a substance,
conductor A substance through which
heat or electric current flows easily,
cones Light-sensitive cells in the retina of
the eye that enable us to see colours,
constellation A pattern made by a number
of stars when seen from Earth,
convection The transfer of heat through a
fluid by currents within the fluid.

427

GLOSSARY

converging lens See convex lens.
convergent evolution The way in which
different species evolve similar features
because they are subjected to similar
environmental conditions,
convex lens A lens that curves outwards,
coprolites Fossilised dung,
corona The outer layer of hot gases
surrounding the Sun.

corrasion The wearing away of a surface by
the action of rocks carried in ice or water,
corrosion Chemical attack of the surface
of a metal.

cosmology The study of the structure and

origin of the Universe.

cotyledon A simple leaf which forms part

of a developing plant. Also called a seed-

leaf.

covalent bond A chemical bond formed by
atoms sharing one or more electrons.

CPU Central processing unit. The “brain”
of a computer.

cracking The process of splitting larger
molecules into smaller ones by heating
under pressure.

cross-fertilization Fertilization of a plant
with gametes from another species of plant,
crust The rocky outer surface of the Earth,
crystal A solid substance with a regular
shape.

crystal lattice The repeating pattern of
atoms or ions that forms a crystal,
crystallogram A pattern formed on a
photographic plate by passing a beam of
X-rays through a crystal.
cyclone Another name for a huriicane
especially over the Indian Ocean,
cytoplasm The contents of a cell , except
the nucleus.

decant To separate a mixture of a solid
and a liquid by allowing the solid to settle
and pouring off the liquid,
decibel A unit used to measure the
loudness of a sound,
decomposer A tiny organism, such as a
bacterium, which breaks down dead matter,
decomposition 1. Organic decay.

2. Breaking larger molecules into smaller
ones.

density The mass per unit volume of a
substance.

depression An area of low air pressure,
which often brings bad weather,
dermis The thick layer of tissue in the skin
below the epidermis.

desalination The removal of salt from sea
water.

desertification The formation of a desert,
desiccate Dry out a substance by removing
water from it.

desiccator A sealed container used to
desiccate and keep substances dry.
detector The circuit in a radio receiver
that separates a sound signal from a radio
wave.

detergent A substance which, when added
to water, helps the water to remove grease
and oil.

dicotyledon A flowering plant with two
cotyledons.

diffraction The spreading out of waves,
e.g. light waves, when they pass through a
narrow slit.

diffusion The mixing of two or more
different substances because of the
random movement of the molecules,
digestion The breaking down of food in
the stomach into simple molecules which
can pass into the bloodstream,
digital Representing a quantity by
electrical signals which are either on or off.
(Compare to analogue.)
diode An electronic component that lets
electricity flow in one direction only,
diploid cell A cell with two complete sets of
chromosomes.

direct current (DC) An electric current
that flows in one direction only.

(Compare to alternating current.)
discharge The release or conversion of
stored energy.

displacement A chemical reaction in

which one kind of atom or ion in a molecule

is replaced by another.

distillation A process in which a liquid is

boiled and then condensed. It is used to

separate mixtures of liquids or purify

liquids.

DNA Deoxyribonucleic acid. The
chemical which makes up chromosomes and
is present in all cells. DNA can replicate
itself to transmit genetic information from
parent to offspring.

doldrums Area along the Equator where
the trade winds meet and form an area of
very little wind.

drag The force that slows down an object
as it travels through a liquid or gas.
drought A long period with no rain,
dye A substance which colours a material,
dynamo A generator that produces direct
current.

Easterlies Major winds which blow from
the east.

echo When a sound is heard again
because it reflects off a solid object,
eclipse The shadow caused by a body
blocking the light from another. See lunar
eclipse and solar eclipse.
ecology The study of the relationships
between organisms and their environment,
ecosystem A distinct area in the biosphere
which contains living things, e.g. a lake or
a forest

effort A force applied to move a load,
elasticity The ability of a material to
stretch and then return to its original
shape.

electrode A piece of metal or carbon that
collects or releases electrons in an electric
circuit.

electric current The flow of electrons or
ions.

electrolysis Chemical change in an
electrolyte caused by an electric current
flowing through it.

electrolyte A substance that conducts
electricity when molten or in solution.
electromagnetic spectrum The complete
range of electromagnetic radiation -
gamma rays. X-rays, ultraviolet radiation,
visible light, infrared radiation, microwaves,
and radio waves.

electromotive force (e.m.f.) The potential
difference of a battery or cell. It pushes an
electric current around a circuit.

electron A particle with a negative
electrical charge outside the nucleus in all
atoms.

electron gun A device which produces a
stream of electrons, called a cathode ray, for
use in a television, for example,
electron micrograph A magnified image
of an object made by an electron microscope.
electron microscope A microscope that uses
a beam of electrons to produce a magnified
image of an object.

electrophoresis The separation of charged
particles in a mixture,
electroplating The coating of a metal
object with a thin layer of another metal by
electrolysis.

electroscope An instrument that detects
electric charge.

electrostatic field The field of force
surrounding an electrically charged object,
element A substance which cannot be
broken down into more simple substances
by chemical reactions.
emulsifier A substance used to make
immiscible liquids blend,
emulsion Tiny particles of one liquid
dispersed in another liquid,
endoplasmic reticulum (ER) A system of
membranes in a cell on which chemical
reactions take place,
endoscope An instrument used to
examine the inside of the body,
endoskeleton The internal skeleton of
vertebrates,

endosperm The tissue in a seed that stores
food.

endothermic reaction A chemical reaction
during which heat is absorbed from the
surroundings.

energy The capacity to do work.
environment The surroundings of an
animal or plant.

enzyme A catalyst in living things that
increases the speed of reaction in natural
chemical processes,
epidermis The outer layer of the skin.
Equator An imaginary circle around the
middle of the Earth, midway between the
Noth and South Poles,
equilibrium A state of physical or
chemical balance.

erosion The wearing away of the Earth’s
surface due to the effects of weather,
water, or ice.

erythrocytes Red blood cells.
escape velocity The minimum speed that
a space rocket must reach to escape the
Earth’s gravity.

eukaryotic cell A cell with a nucleus.
(Compare to prokaryotic cell.)
eutrophication Where an excess of
nutrients, from fertilizers for example,
gets into water, causing the overgrowth of
aquatic plants. This creates a shortage of
oxygen in the water, killing animal life,
evaporation The changing of a liquid into
a vapour by the escape of molecules f rom its
surface.

evolution The gradual process by which
life develops and changes,
evolve To undergo evolution,
excretion The elimination of waste by
organisms.

exosphere The outermost part of the

Earth’s atmosphere, about 900 km

(560 miles) above the surface of the Earth.

428

GLOSSARY

exoskeleton The hard outer “skin” of
many invertebrates , such as insects,
exothermic A chemical reaction which
produces heat,

extinction The death of all the members
of a species.

fault A break in the Earth’s crust.
fermentation The process in which yeast
converts sugars in plant material to alcohol
and carbon dioxide,
fertilization The joining of male and
female gametes.

fibre An elongated, thick-walled plant cell.
filter A device that removes the solid
material from a liquid,
fluid A substance which can flow, i.e.
either a gas, a vapour, or a liquid,
fluorescence Light given off by certain
atoms when they are hit by ultraviolet
radiation.

FM Frequency modulation. The
transmission of a signal by changing the
frequency of the carrier wave, such as a radio
wave.

fold A bend in rock layers.

food chain A series of organisms , each of

which is eaten by the next.

food web The system of food chains in an

ecosystem.

force Something which changes the
movement or shape of an object,
force field The area in which a force can
be felt.

formula (plural formulae) A set of
chemical symbols which shows the make¬
up of a chemical.

fossil The remains of an animal or plant
turned to stone.

fossil fuel A fuel which has been formed
over millions of years from the remains of
living things, e.g. coal and oil.

Fraunhofer lines Dark lines on the Sun’s
spectrum caused by elements in the Sun’s
gases absorbing certain wavelengths of
light.

freezing point The temperature at which a
substance turns from liquid to solid,
frequency The number of waves that pass
a point every second.

friction A force which slows down or stops
the movement of one surface against
another.

front The first part of an advancing mass
of cold or warm air.
fuse A safety device used in electrical
circuits. It is a thin wire which melts if too
much current passes through it.

Gaia (Say guy-a) hypothesis The theory
that all the living things on the Earth form
a huge “ organism ” which controls the
biosphere.

galaxy A large group of stars, dust, and
gas, all loosely held together by gravity.

Our galaxy is called the Milky Way.
galvanize To coat iron with zinc to protect
it from rust.

gamete A reproductive cell , such as a
sperm or egg.

gamma rays A type of electromagnetic
radiation with a very short wavelength.

ganglion (plural ganglia) A group of nerve
cells enclosed in a casing of connective
tissue.

Geiger counter An instrument used to
detect and measure certain forms of
radiation.

gene Part of the chromosome which
controls a particular characteristic of an
individual.

generator A device which converts
mechanical energy into electricity,
geochemistry The study of the chemistry
and composition of the Earth,
geomorphology The study of the physical
features on the Earth’s surface,
geothermal energy Energy harnessed from
the hot rocks inside the Earth,
germination The early stages in the growth
of a seed.

gland An organ or group of cells which
produces substances used by the body,
global warming The heating of the Earth’s
atmosphere caused by the greenhouse effect.
gluons Particles within protons and
neutrons that hold quarks together,
gravity The force of attraction between
any two masses. It is what attracts all objects
towards the Earth, giving them weight.
greenhouse effect The way in which
certain gases in the Earth’s atmosphere ,
especially carbon dioxide, trap heat. The
build up of these gases leads to global
warming .

grike An enlarged crack in limestone
produced as the rock gradually dissolves in
rainwater.

groynes Low walls or fences built along
the seashore to prevent coastal erosion.
guttation The loss of water from the
surface of a plant as liquid rather than
vapour.

gyroscope A fast-spinning wheel whose
axis stays pointing in the same direction,
once it is spinning. A gyrocompass is used
in the navigation of ships and aircraft.

habitat The natural home of an animal or
plant.

haemoglobin A compound in red blood
cells which carries oxygen around the body,
haploid cell A cell with a single set of
chromosomes.

hard water Water which contains calcium

and magnesium salts.

hardware The mechanical and electronic

parts of a computer.

hemisphere One half of a sphere. The

Earth is divided into the Northern and

Southern Hemisphere by the Equator.

herbivore A plant-eating animal.

Hertz (Hz) The unit of frequency. One
Hertz is one cycle per second,
hibernation The deep sleep or period of
inactivity that some animals go into during
the winter.

holography A method of producing a
three-dimensional image of an Object on
a flat surface, using a split beam of laser
light.

homeostasis The way an animal keeps it
internal environment (temperature, blood
pressure, etc.) stable,
hominid Any member of the primate
family Hominidae, including humans.

hormones Chemical “messengers” which
move around in the blood stream and
control the functions of the body,
humidity The amount of water vapour in
the air.

hurricane A huge, circular tropical storm
in which there are wind speeds of
120 km/h (75 mph) or more,
hydraulic Describes a machine that
operates by transferring pressure through
a liquid.

hydrocarbon A chemical compound made
up of hydrogen and carbon only,
hydroelectricity The generation of
electricity by harnessing the energy in
flowing water.

hydrometer An instrument used to
measure the density of a liquid,
hyphae (say hi-fee) (singular hypha) Tiny
threads that form the main body of a
fungus.

igneous rock Rock formed when molten
magma cools and solidifies,
immiscible Describes two liquids which do
not blend together, e.g. water and oil.
indicator A substance which shows the pH
of a solution by its colour,
induction The production of an electric
current by a changing magnetic field.
industrial plant The land, buildings, and
machinery used to carry out an industrial
process.

inertia The tendency of an object to
remain at rest or keep moving in a straight
line until a force acts on it.
infrared radiation (IR) The type of
electromagnetic radiation produced by hot
objects.

inhibitor A substance that slows down a
chemical reaction.

inorganic Not created by natural growth.
(Compare to organic .)
inorganic chemistry The branch of
chemistry which deals with chemicals
except those that contain carbon.
(Compare to organic chemistiy.)
input Information fed into a computer,
insulator A material that reduces or stops
the flow of heat, electricity, or sound,
integrated circuit A tiny electric circuit
made of components built into the surface
of a silicon chip.

interference The disturbance of signals
caused where two or more waves meet,
interglacial The period of warmer weather
between two ice ages,
internal reflection The reflection of some
of the light in a ray that passes from a dense
to a less dense medium, e.g. from glass to
air.

invertebrate An animal with no backbone,
inverter A device used to convert direct
current into alternating current.
ion An atom or group of atoms that has
lost or gained one or more electrons to
become electrically charged,
ionic bond A chemical bond made when
one or more electrons are passed from one
atom to another, forming two ions of
opposite charge which attract each other,
ionosphere The part of the atmosphere,
from 50-400 km (30-250 miles) above the
Earth’s surface, that reflects radio waves.

429

GLOSSARY

irradiation The use of radiation to preserve
food.

isobar A line on a weather map which
connects points with the same air pressure,
isomers Compounds which contain the
same atoms , but in different arrangements,
isoseism A line on a map connecting
places with equal strengths of earthquake
shock.

isotopes Atoms of the same element which
have the same number of protons, but a
different number of neutrons.

jet propulsion The pushing forward of a
machine by a stream of Jluid.
jet stream Strong winds that circle the
Earth about 10 km (6 miles) above the
surface.

joule (J) A unit of energy.

Kelvin scale See absolute scale.
keratin A protein which makes up hair,
horns, hoofs, nails, and feathers,
kinetic energy The energy which an object
has because of its movement.

laccolith A mass of igneous rock which
pushes the rock above into a dome shape,
lactose A sugar that occurs in milk,
larva (plural larvae) The second stage in
the life of an insect, between the egg and
the adult (e.g. a caterpillar),
laser Light Amplification by the
Stimulated Emission of Radiation. A device
that emits an intense beam of light,
latent heat The heat needed to change a
solid to a liquid or a liquid to a gas without
a change of temperature,
latitude A measure of distance from the
Equator (the Poles are at 90° latitude and
the Equator is at 0°). Lines of latitude are
imaginary lines drawn around the Earth,
parallel with the Equator.

LDR Light-dependent resistor. A resistor
whose resistance increases when the amount
of light which hits it increases,
leaching The extraction of a soluble
material from a mixture by passing a solvent
through the mixture.

LED Light-emitting diode. A diode which
emits light when a current flows through it.
leucocytes White blood cells,
lift The upward force produced by an
aircraft’s wings which keeps it in the air.
ligaments Shorthands of flexible tissue
which connect bones together in joints,
light year The distance travelled by light in
a year. It is equal to 9.5 million, million km
(5.9 million, million miles),
lignin A polymer in the walls of the cells of
trees and shrubs. It makes the plant woody,
lithosphere The layer of the Earth that
includes the crust and the upper mantle.
longitude A measure of distance around
the Earth, measured in degrees. Lines of
longitude are imaginary lines drawh on the
Earth’s surface between the Poles,
longitudinal wave A wave in which the
particles of the medium vibrate in the
direction in which the wave is travelling.

luminosity The amount of light given out
by an object, such as a star,
lunar eclipse When the moon moves into
the Earth’s shadow so that it cannot be
seen from Earth.

lymphocytes White blood cells which fight
disease.

lymphatic system A network of tubes and
small organs which carries a fluid called
lymph from the body’s cells into the
bloodstream.

magma Liquid molten rock in the Earth’s
mantle and crust. It cools to form igneous
rock.

magnetic field The area around a magnet
in which its effects are felt,
magnetic poles The two points on a
magnet where magnetic effect is strongest,
magnetism The invisible force of
attraction or repulsion between some
substances, especially iron,
magnetosphere The magnetic field around a
star or planet.

manned manoeuvring unit (MMU) A

backpack used by astronauts to move about
in space.

mantle A thick, dense layer of rock under
the Earth’s crust.

mass The amount of matter in an object,
matter Anything that has mass and
occupies space.

meiosis Cell division which produces four
gametes , each of which has half the number
of chromosomes as the original cell,
melanin A brown pigment found in the
skin, hair, and eyes.

melting point The temperature at which a

solid turns to a liquid.

membrane A thin skin.

meniscus The curved upper surface of a

liquid in a thin tube.

Mercalli scale The scale used to measure
an earthquake’s intensity,
mesopause The part of the atmosphere
about 80 km (50 miles) above the Earth’s
surface. It is the upper limit of the
mesosphere.

mesosphere The part of the atmosphere
from about 50-80 km (30-50 miles) above
the Earth’s surface.

metal Any of several elements that are
usually shiny solids and good conductors of
electricity and heat,
metallic bond A bond formed between
metal atoms. The metal’s electrons flow
freely around the atoms,
metamorphic rock Rock that has been
changed by great heat and pressure
underground.

metamorphosis A change of form, e.g.
from a caterpillar to a pupa.
meteor A tiny piece of dust from space,
which burns up as it enters the Earth’s
atmosphere , producing a streak of light,
meteorite A piece of rock or metal from
space which enters the Earth’s atmosphere
and reaches the ground without burning

up-

meteorology The study of the weather.

microclimate The particular climate of a

small area, e.g. a valley.

micrograph A photograph taken using a

microscope.

microorganism A tiny organism which can
be seen only with the aid of a microscope.
microscope An instrument that enlarges
the image of an object through a system of
lenses.

microwave A type of electromagnetic
radiation. Microwaves are very short radio
waves.

migration The movement of some animals
to find food, warmth, space, or a place to
breed.

mimicry Where a species of plant or
animal evolves to look like another,
mineral A naturally occurring substance
not formed from plant or animal material,
e.g. rock and metal,
mineralogy The study of minerals,
mirage An optical illusion produced by
light bending through layers of air with
different densities.

miscible Describes two or more liquids
which can be blended together,
mitochondrion (plural mitochondria) An
organelle that produces energy for a cell,
mitosis Cell division where the nucleus
divides to produce two cells, each with the
same number of chromosomes as the parent
cell.

mixture A substance which contains two
or more elements or compounds which are
not combined chemically,
modulation The transmission of a signal
by changing the characteristics of a radio
wave (called the carrier wave),
mole The amount of a substance that
contains the same number of atoms or
molecules as there are in 12 g (0.4 oz) of
carbon-12.

molecule The smallest unit of an element
or compound. A molecule is made up of at
least two atoms.

momentum The tendency of a moving
object to keep on moving until a force
stops it. See also inertia.
monocotyledon A flowering plant with a
single cotyledon. See also dicotyledon.
monomer A molecule that is the building
block of a polymer.

monsoon A strong wind that changes
direction according to the season,
bringing torrential rain from the sea to
areas such as India and Bangladesh,
moon A small body that orbits a planet,
moraine Rocks and debris that have been
deposited by a glacier,
mordant dyes Dyes that need another
chemical to be added to fix them to a
fabric.

mouse A hand-held device that is used to
control a cursor on a computer monitor,
mutation A random change in the
chromosomes of a cell,
myelin A fatty material found around
nerve fibres.

myofibril Stretchy threads found in
muscle cells.

natural selection The process by which the
characteristics that help a species to survive
are passed on to the next generation,
nebula (plural nebulae) A cloud of dust
and gas in space.

nectar A sugary liquid found in the
flowers of some plants.

430

GLOSSARY

nematocyst A long, coiled thread which
shoots out of a stinging cell , e.g. in a sea
anemone.

nerve Part of a network of tiny “cables”
that pass messages from the body to the
brain and from the brain to the muscles,
neuron A nerve cell
neutralize Make an acid or alkali into a
neutral solution, i.e. make it neither acid
nor alkaline.

neutron A particle in the nucleus of an
atom which has no electrical charge,
newton (N) A unit of force,
niche (say neesh) The position that a
living thing occupies in an ecosystem.
nocturnal An animal which is active at
night and sleeps during the day.
nuclear fission A nuclear reaction in which
the nucleus of an atom splits into two
smaller nuclei, releasing energy,
nuclear fusion A nuclear reaction in which
the nuclei of light atoms (e.g. hydrogen)
fuse to form a heavier nucleus, releasing
energy.

nuclear reaction A change in the nucleus of
an atom.

nucleolus A small, dense, round body

inside the nucleus of a cell.

nucleus 1. The central part of an atom,

made up of protons and neutrons. 2. A

body found in most plant and animal cells

that contains the genetic material of the

cell.

nutrients Substances in f ood which are
used by plants and animals for growth.

observatory A building from which
astronomers study space,
occlusion Where a cold front catches up
with a warm front.

ohm (Q) A unit of electrical resistance.
okta scale A scale for measuring cloud
cover. One okta equals one-eighth cloud
cover.

omnivore An animal that eats both plants
and animals.

opaque Does not let light through,
optical fibres Thin glass fibres along
which light travels. They are used in
communications.

orbit The path of one body, such as a

planet or satellite, around another body,

such as a star or planet.

ore A naturally occurring rock from which

metals can be extracted.

organ A self-contained part of an organism

with a special function, e.g. the brain and

the heart.

organelle Specialized structure that forms

part of a plant or animal cell.

organic 1. A compound containing

carbon. 2. Food production without the

use of chemical fertilizers.

organism A living thing consisting of one

or more cells.

oscillator An instrument that produces an
alternating current of known frequency.
oscilloscope An instrument that shows
electrical signals on a screen,
osmosis The movement of water through
a semi-permeable membrane from a weak
solution to a strong one.
ossify Turn to bone,
output Information from a computer.

oxidation When a substance gains oxygen
or loses hydrogen, or an atom loses
electrons in a chemical reaction.
oxide A compound formed between an
element and oxygen,
oxidizing agent A substance that causes
the oxidation of another substance,
ozone An allotropeoi oxygen found in the
Earth’s upper atmosphere , where it forms
the ozone layer. A molecule of ozone
contains three oxygen atoms.

parabolic dish A specially shaped dish that
collects and concentrates waves, such as
sound or electromagnetic waves,
parallax The apparent movement of
objects against each other as the observer
moves, e.g. the movement of nearby trees
against background hills,
parasite An organism that lives on and
feeds off another organism, called the
host, often until it destroys the host,
particle A tiny speck of matter.
parthenogenesis Reproduction without
mating.

pasteurization The heating of food to
destroy disease-carrying bacteria,
payload The equipment, e.g. a satellite,
carried into space by a spacecraft,
penumbra A partial shadow, especially
round the shadow of the moon or Earth in
an eclipse.

periodic table A table of all the elements
arranged in order of their atomic numbers.
pesticide A substance used to kill pests
such as insects.

petrochemical Any chemical made from

petroleum or natural gas.

petrology The study of rocks.

pH A measure of acidity or alkalinity of a

solution.

phases 1. The changes in the apparent
shape of a moon or planet caused by the
reflection of sunlight. 2. The three states
in which matter occurs - solid, liquid, and
gas or vapour.

pheromones Chemical substances released
by an animal to communicate with another
by smell.

phloem Tissue that carries food in a plant,
photocell An electronic device which
generates electricity when light falls on it,
e.g. in a solar-powered calculator,
photochromic The ability of an object, e.g.
a spectacle lens, to darken or change
colour when exposed to light, and to
return to its original colour when the light
is removed.

photoelectric effect The emission of
electrons f rom the surf aces of some
substances when light hits them,
photon The particle which makes up light
and other electromagnetic radiation.
photosphere The visible surface of the
Sun, which gives out almost all of its
light.

photosynthesis The method by which
plants make food from water and carbon
dioxide using energy from the Sun.
physics The science of the properties and
nature of matter and the interactions of
energy and matter.

physiology The study of how organisms
work.

phytoplankton Tiny plants which are part
of plankton.

piezoelectric effect The production of
electricity by applying stress to certain
crystals , e.g. quartz.

pigment A substance that gives colour to a
material, but unlike a dye , does not dissolve
in it.

pitch The property of a sound that makes
it high or low.

placebo (say plas-see-bo) An inactive

substance given to a patient to compare its

effects with a real drug.

planet A large body that orbits a star.

plankton Tiny plants and animals which

live near the surface of the seas and inland

waters.

plant Any organism that contains
chlorophyll.

plaque (say plark) A deposit on teeth

where bacteria thrive.

plasma 1. The liquid part of the blood.

2. A hot, electrically charged gas, in which
the electrons are free from their atoms,
platelet An irregular-shaped disc in the
blood which releases chemicals to
coagulate the blood,
plate tectonics The study of continental
drift and the spreading of the sea floor,
polar reversal The reversal of the
direction of the Earth’s magnetic field.
pollution Substances, such as waste
chemicals from factories, that dirty or
poison the air, land, and water,
polymer An organic compound that has
very long molecules, made up from many
monomers.

potential difference The difference in
energy between two places in an electric
field or circuit.

potential energy 1. Energy stored for use
at a later time. 2. The stored energy that a
body has because of its position or state.*
power The rate of change of energy,
precipitate Tiny particles of solid in a
liquid, made by a chemical reaction.
precipitation Rain, snow, sleet, or hail,
predator An animal which lives by hunting
and eating other animals,
pressure The amount of force pushing on
a given area.

prey An animal that is hunted or eaten by
another animal.

prism A block of transparent material e.g.
glass with a triangular cross-section,
program A series of coded instructions to
operate a computer,
prokaryotic cell A cell with no nucleus.
prominence A mass of glowing gas
reaching out from the surface of the Sun.
protein A substance found in foods such
as meat, fish, cheese, and beans, which the
body needs for growth and repair,
proton A particle in the nucleus of an
atom which has a positive electric charge,
protostar A gas cloud about to turn into
a star.

pulsar A dense star which emits regular
pulses of radiation , usually radio waves.

qualitative analysis Finding out what a
substance is made of.
quantitative analysis Finding out how
much of each ingredient is in a substance.

431

GLOSSARY

;

quantum theory The theory that light and
other electromagnetic radiation is made up
of a stream of photons, each carrying a
certain amount of energy,
quark (say kwark) One of a group of small
particles that make up protons and neutrons.
quasar (say kway-zarj The brilliant core of
a young galaxy, probably a disc of hot gas
around a massive black hole.

radar Radio detection and ranging. A way
of detecting objects by sending out radio
waves and collecting the “echoes”,
radiation 1. An electromagnetic wave.

2. A stream of particles from a source of
radioactivity. See also electromagnetic
spectrum.

radioactive dating A method of estimating
the age of an object by measuring how
much the radioactive isotopes in it have
decayed.

radioactivity The disintegration of the
nuclei in an atom, causing radiation to be
given off.

radiosonde A package of instruments
carried into Earth’s upper atmosphere by a
weather balloon to gather meteorological
information.

RAM Random access memory. Computer
memory chips where information can be
stored and retrieved. The information is
lost when the computer is turned off.
rarefaction Areas along a longitudinal
wave, such as a sound wave, where the
pressure and density of the molecules is
decreased. (Compare to compression.)
reactants The substances which take part
in a chemical reaction.
reaction 1. A force that is the same in
magnitude, but opposite in direction to
another force. Every force has a reaction.

2. (Chemical reaction) Any change that

alters the chemical properties of a

substance or that forms a new substance.

reactivity The ability of a substance to take

part in a chemical reaction.

real image An image formed where light

rays focus. It can be seen on a screen.

(Compare to virtual image.)

recycling Using waste material again, thus

saving resources and energy.

red giant A star near the end of its life,

which has swelled and cooled.

red shift The stretching out of light

(moving it towards the red end of the

spectrum) from a galaxy moving away from

the Earth.

reducing agent A substance that causes the
reduction of another substance,
reduction When a substance gains
hydrogen or loses oxygen, or an atom
gains electrons in a chemical reaction.
reflection The bouncing back of light,
heat, or sound from a surface,
reflex An automatic reaction to
something.

refraction The change of direction of a
light beam as it passes from one medium
to another of different density , e.g. from air
to glass.

refractive index The ratio of the speed of
light in one medium to the speed of light
in a second medium when a light ray is
refracted.

resistance A measure of how much an
electrical component opposes the flow of
an electric current.

resistor A component in an electric circuit

that opposes the flow of electricity.

resonance When the vibrations of an object

become large because it is being made to

vibrate at its “natural” frequency.

resource A substance that can be used to

make or do something useful. Oil and coal

are natural resources.

respiration The process in which oxygen

is taken in by living things and used to

break down food. Carbon dioxide and

energy are produced.

resultant The overall force which results

from two or more forces acting on an

object.

reverberation Where an echo reaches a
listener before the original sound has
finished. It makes a sound seem to last
longer.

rheostat A resistor whose resistance cm be
changed.

ria (say ree-a) A long, narrow sea inlet
caused by the flooding of a river valley,
ribosomes Tiny spherical bodies in the
cytoplasm of cells, where proteins are made.
Richter (say rik-tur) scale A scale used to
measure the strength of earthquakes,
robot A machine that performs jobs
automatically.

ROM Read only memory 7 . Computer
memory in which information is stored
permanently, so that it can be retrieved,
but not altered.

salt 1. A compound formed from the
reaction of an acid with a base. 2. The
common name for sodium chloride,
sap The liquid that flows through a plant,
carrying food and water,
saprophyte An organism, such as a fungus
or bacterium, that lives on dead or
decaying matter.

satellite An object which orbits a planet.
There are natural satellites, e.g. a moon,
and artificial satellites, e.g. a craft used for
reflecting radio signals,
satellite dish A dish-shaped aerial which
receives signals broadcast from satellites,
saturation When no more solute can be
dissolved in a solution.
scalar quantity A quantity that has only
magnitude, e.g. mass and time. (Compare
to vector quantity.)
secretion The release of specific
substances from plant and animal cells.
sedimentary rock Rock formed when
fragments of material settle on the floor of
a sea or lake in layers and arc cemented
together over time.

seismic wave A wave that travels through
the ground, e.g. from an earthquake or
explosion.

seismometer A device that records
vibrations in the ground, such as those
caused by earthquakes,
semiconductor A substance which has a
resistance somewhere between that of a
conductor and an insulator.
semipermeable membrane A membrane
which lets small molecules through, but
stops large molecules.

sessile 1. Describes animals that cannot
move around, e.g. sea anemones.

2. Describes plants with no stalks e.g. algae,
sex cell See gamete,
sexual reproduction Reproduction that
involves the combination of male and
female gametes.

sial The silica- and aluminium-rich upper

layer of the Earth’s crust.

silica A white or colourless compound of

silicon that occurs naturally, eg quartz.

sima The silica- and magnesium-rich lower

layer of the Earth’s crust.

skeleton The frame of bone and cartilage

in vertebrates which supports the body and

protects its organs.

smog A poisonous mixture of smoke and
fog.

soft water Water free of dissolved calcium
and magnesium salts,
software The programs used by a
computer.

solar constant The amount of heat energy
from the Sun which hits a certain area of
the Earth’s surface.

solar eclipse An eclipse in which the moon
passes between the Earth and the Sun so
that the Sun, or part of it, cannot be seen
from Earth.

solar flare A sudden burst of radiation
from the Sun.

solar panel An object which collects
energy from the Sun and uses it to heat
water, for example, or to produce
electricity.

Solar System The Sun, the planets that
orbit the Sun, their moons, and the other
bodies in space whose movements are
controlled by the Sun’s gravity,
solder An alloy (often made of tin and
lead) used to join metal surfaces together,
solenoid A coil of wire which produces a
magneticJield when an electric current flows
through it.

solubility The ability of a solute to be
dissolved.

solute The substance which dissolves in a
solvent to form a solution.
solution A mixture in which the molecules
of a solute me mixed with the molecules of
a solvent.

solvent The substance (usually a liquid) in
which a solute dissolves to form a solution.
sonar Sound navigation and ranging. A
way of detecting objects and of navigating
underwater by sending out sound waves,
sonic boom The loud explosive noise
made by the shockwave from an object
travelling faster than the speed of sound,
space age The era of space travel,
space probe An unmanned spacecraft sent
from Earth to investigate the Solar System.
space station A spacecraft, big enough for
people to live and work on, which orbits the
Earth.

species A group of organisms which look
alike and can breed with one another,
spectroscope An optical instrument which
divides the light given off by an object into
its spectrum.

spectrum (plural spectra) A particular

distribution of wavelengths and frequencies,
e.g. the electromagnetic spectrum.
specular reflection When light bounces
off a surface at exactly the same angle as
that at which it hits.

iM £§&$> ‘t ■

432

l——-i--i—--i--

«rv -ri’SK ,- S ^ W J ~

L * ■ * • *. .. - ’ ' ' * - p ’ 1 "* ■ ••• ... v.p*.. ' i

GLOSSARY

spinal cord A bundle of nerves running
from the brain down through the spine,
star A celestial body that releases energy
from the nuclear reactions in its core,
starch A polymer found in plants which is
an important part of the human diet,
static electricity An electric charge held on
an object, caused by the gain or loss of
electrons.

sterilization The removal of bacteria from
an object.

stoma (plural stomata) A tiny opening in a
plant’s leaf or stem through which gases
and water vapour pass,
stratigraphy The study of rock layers,
stratopause The boundary between the
stratosphere and the mesosphere in the Earth’s
atmosphere.

stratosphere The part of the Earth’s
atmosphere between the troposphere And the
mesosphere.

subatomic particle A particle smaller than
an atom , e.g. a proton or a neutron,
sublimation When a solid turns straight
from a solid into a gas without becoming a
liquid first.

substance Any kind of matter.
succession The process of change from
one ecosystem to another, eg from grassland
to woodland.

sugars A group of soluble, sweet-tasting
carbohydrates.

sunspot A cooler patch on the Sun’s
surface which appears darker than its
surroundings.

superconductor A substance that has no
electrical resistance at very low
temperatures.

supernova (plural supernovae) The

explosion of a very large star at the end of
its life.

supersonic Faster than the speed of
sound.

surface tension An effect that makes a
liquid seem as though it has an elastic
“skin”. It is caused by cohesion between the
surface molecules.

suspension A mixture of tiny particles of
solid matter in a liquid,
synapse A junction of two nerve cells .
synthesis The building of larger molecules
from smaller molecules or atoms,
synthesizer A musical instrument that
creates sound electronically.

temperate Describes a climate which has
mild summers and cool winters,
temperature A measure of how hot or cold
something is.

terminal A connecting point on an

electrical component.

thermal A current of rising hot air in the

atmosphere.

thermistor A rcs^/orwhose resistance
changes with temperature,
thermoplastic A material which can be
repeatedly softened by heating and
hardened by cooling,
thermoset A soft material which sets hard
when heated.

thermosphere A part of the Earth’s
atmosphere between the mesosphere and the
exosphere.

timbre The quality of a musical sound.

tissue A group of similar cells which carries
out a function, e.g. muscle tissue,
titration A method of finding the
concentration of a solution,
trace elements Substances, such as
minerals, that are needed by living things
in minute amounts.

trachea The main tube which carries air to
and from the lungs,
trade winds Winds that blow steadily
towards the Equator from the northeast
and southeast.

transformer A device that increases or
decreases voltage.

translocation The movement of fluids
through a plant.

translucent Allows some light through, but
is not “see-through”,
transparent Allows nearly all light
through, so that it is “see-through”,
transpiration The loss of water from a
plant by evaporation.
transverse wave A wave in which the
particles of the medium vibrate at right
angles to the direction of travel of the
wave.

trophic level The level at which an animal
is in a food chain.

tropical Describes a climate which is hot
with periods of heavy rainfall,
tropopause The boundary between the
troposphere and the stratosphere.
troposphere The lowest layer of the
Earth’s atmosphere , between the surface and
the stratosphere. It is about 13 km
(8 miles) thick on average,
turbine A machine which is made to rotate
by a Jluid in order to drive a generator.
typhoon The name given to a hurricane in
the Pacific Ocean.

UHF Ultra-high-frequency radio waves,
ultrasound Soundwitha frequency above
that which the human ear can detect,
ultraviolet (UV) A type of electromagnetic
radiation with a wavelength shorter than
visible light.

umbra The dark central part of a shadow,
where no light falls.

Universe The whole of space and
everything it contains.

upthrust The upward push on an object in
a fluid.

vacuole A small fluid-idled sac in the
cytoplasm of a cell.

vacuum A space in which there is no
matter.

valency The number of chemical bonds
that an atom can make with another atom,
vector quantity A quantity which has both
magnitude and direction, e.g. a force.
(Compare to scalar quantity.)
veins Tubes which carry blood from all
parts of the body back to the heart,
velocity Speed in a particular direction,
vertebrate An animal with a spine.

VHF Very-high -frequency radio waves,
vibration A quick back-and-forth
movement. For example, an earthquake
causes the Earth to vibrate; sound causes
the air to vibrate.

virtual image An image formed where
light rays appear to be focused, e.g. a
reflection in a mirror. (Compare to real
image.)

virus A microscopic particle which invades
cells to reproduce, and often cause disease,
viscosity A measure of how easily a
substance flows.

vitamin An organic compound found in
foods which is essential for good health,
volt The unit of potential difference.
voltaic cell See cell

voltmeter or voltammeter A device used to

measure potential difference.

volume 1. The space occupied by matter.

2. The loudness of a sound,
vulcanization The hardening of rubber by
heating it with sulphur.

waterspout A column of water sucked up
by a tornado moving over the sea.
watt (W) A unit of power (1 watt = 1 joule
per second).

wavelength The distance between the crest
of one wave and the crest of the next,
weight The force with which a mass is
pulled towards the centre of the Earth.
Westerlies Major winds blowing from the
west.

whirlwind A column of air spinning
rapidly in a funnel shape over land or
water.

white dwarf The small, dense remains of a
dead star.

WMO World Meteorological Organization
work The energy transferred when a force
moves an object or changes its shape.

X-ray A type of electromagnetic radiation
with a wavelength shorter than ultraviolet
radiation.

xylem (sayzy-lem) The tissue which
carries water through a plant.

zeolite A natural or synthetic compound
with an open structure that can act as a
catalyst or a filter for individual molecules.
zeugen A ridge of hard rock formed by
erosion.

zodiac The 12 constellations that are seen in
the sky.

zooplankton The tiny, often microscopic,
animals in the sea which form part of
plankton.

433

INDEX

Page numbers in bold type
refer to main entries.
Numbers in italics refer to
pages in the Fact Finder

absorption, sound 184-5
absorption lines, star
spectra 278
acacia trees 379
acceleration 119
acetylene 44
acid rain

causes 64, 69, 424
liming fields 71
pollution 68, 373
weathering 231
acids 68-9
bases 70

measuring acidity 72
salts 73
acoustics 184
actinium 37
activation energy 52
Adamson, George 393
Adamson,Joy 393
adders 359
additives, food 93
adhesion 128
adhesives 106
ADP (adenosine
diphosphate) 43, 346
adrenaline 104, 105
advection fog 263
aerial photographs 240
aerials 165, 167
aerobic respiration 77,

346

aerofoils 128, 357
aestivation 381
Africa

continental drift 215
droughts 265
grasslands 392
rift valley 218
African palm swifts 333
Agassiz, Louis 229
agoutis 394
agriculture see farming
AIDS 312
air

air masses 253
breathing 347
chemistry' of 74
molecules 50
music 186
nitrogen 42
oxvgen 44

pollution 74, 112, 249
resistance 119,121
sound waves 180
temperature 251
vibrations 182
in water vapour 75
see also atmosphere
air conditioning 141
air pressure 127,250
fronts 253
tornadoes 259
vibradons 178
winds 254
aircraft

acceleration 119
air pressure 127
flight 114

flight simulators 175
jet engines 144
metal alloys 88
sonic boom 177,179

“spaceplanes” 299
vapour trails 261
weather forecasting 271
wings 128
airships 47
Airv, G.B. 218
Alaska 245, 383
albedo 251
albino mutation 364
alchemy 17,60
alcohol

breathalysers 65
fermentation 80, 93
Aldrin, Buzz 302
algae 316
blue-green 307
classification 420
pink snow 266
and pollution 375
reproduction 367
aliphatics 41
alkali metals 33, 34
alkaline-earth metals 35
alkalis 70-1
industry 94

measuring alkalinity 72
alkanes 406
alkenes 406
alligators 331,389
alloys 38, 59, 88
semimetals 39
steel 85
alpha ravs 26
Alps 254, 384
alternating current 159,

160

alternators 159
altitude 250
aluminium 87
alloys 38
anodizing 67
Periodic Table 33
reactivity 66, 405
recycling 112
alveoli 347
amalgam 88
amber 145, 225, 317
amino acids 307, 345
ammeters 152
ammonia 90, 96, 307
ammonites 225
ammonium hydroxide 71
amoebas 314,338
Ampere, Andre-Marie 153
amperes (amps) 148, 153
amphibians 328-9
classification 421
internal environment 350
lifespans 422
amplifiers
electronics 169
radio 164, 165
television 166
amplitude

soundwaves 180,181
vibrations 126
amplitude modulation (AM)
164, 168
anabolism 76
anaerobic respiration 77,
346

anaesthetics 42, 105
analogue signals 171
analogue sound recording
188

analysis, chemical 62-3
AND gates, logic circuits

171 1

Andes Mountains 254, 384
andesitic volcanoes 216
Andromeda galaxy 276, 277

Andronicus 255
anechoic chambers 184
anemometers 256
android barometers 250
angler fish 386
anhingas 389
aniline dyes 41,96
animals

biosphere cycles 372-3
brain 361
breathing 347
burrowing 393
carbon cycle 41
cells 337, 338
classification 310-11,

421

climate and 142
colour and camouflage
380

in deserts 390
digestion 345
evolution 308
extinction 398-9, 425
eyes 204-5
farming 91
feeding 343

food chains and webs 377
fossils 215,225
genetics 364-5
gestation periods 422
grasslands 392-3
groups 378

growth and development
362-3

hearing 182,183
hibernation 381
internal environment
350-1

lifespans 422
metabolic rate 423
migration 381, 425
movement 356-7
muscles 355
nerves 360
nitrogen cycle 42
nutrition 342
oxygen cycle 44
partnerships 379
primates 336
rainforests 394-5
senses 358-9
sexual reproduction 367
skeletons 352-3
sounds 183
teeth and jaws 344
in towns and cities 397
vision 202
wildlife reserves 400
see also human body;
mammals

annelid worms 321, 421
Anning, Mary 225
anodes 67, 168
anodizing 67
Antarctic

continental drift 215
ecology 382
fish 268
ice 229,246
ozone layer 375, 383
temperature 251
winds 255
anteaters 335
antelopes 393
antennae 358, 359
anthers 318
anthropoids 336
antibiotics 105
antibodies 348
anticlines 219
anticyclones 253

antimony 39
antinodes 186
“anti-noise” 181
antioxidants 65, 93
antiseptics 105
ants

formic acid 68
partnerships 379
in rainforests 394
scattering seeds 319
anurans 328
apatite 43, 221
aperture, cameras 206
apes 336
aphids 341,366
apoda 328
Apollo asteroids 294
Apollo spacecraft 287,

299, 301

apparatus, laboratories
405

Appert, N. 93
arachnids 322, 421
arch bridges 117
Archaeopteryx 308
arches, headlands 236
Archimedes 129, 130
Archimedes’ screw 131
Archimedes’ Principle 129
Arctic 375, 382
Arctic terns 382
Arecibo telescope 297
aretes 228
argon
in air 74

Periodic Table 33
uses 48

Ariane rockets 299
Aristarchus 287
Aristotle 31, 120, 177
Armstrong, Neil 302
aromatics 41
Arrhenius, Svante 69
arsenic 39, 63
arteries 349
arthritis 105
arthropods 322-3, 422
artificial selection 309
asexual reproduction 366
Asia

droughts 265
mountains 218
Steppes 393
asphalt 98
aspirin 104, 105
asses, wild 384
asteroids 283, 289, 294
asthenosphere 214
asthma 105
Aston, Francis 63
astronauts 302-3
breathing in space 70
food 92 1

moon landings 287
rockets 299
satellite repair 300
space stations 304
weightlessness 125
astronomy 273, 274, 296
see also space; stars;
Universe
Aswan dam 388
Atacama desert 265, 390,
391

Atlantic ocean 215, 235
atmosphere 248-9, 287
clouds 260-3
fronts 253

greenhouse effect 40,

372

humidity 252

on Jupiter 290
ozone layer 44, 46
pollution 249
radiation 298
on Venus 286
winds 254-6
see also air
atolls 234
atomic bombs 137
atomic clocks 34
atomic number 24, 32-3
atomic emission spectrum
63

atomic structure 24-5
bonding 28-9, 52, 53
compounds 58
counting 53
mass spectrometry 63
nuclear energy 113, 136
oxidation and reduction
64

Periodic Table 32-3,

402-3

photoelectric effect 191
plasma 18
radioactivity 26-7
static electricity 146
ATP (adenosine
triphosphate) 43, 346
Aurora Australis 213
Aurora Borealis 140, 154,
213

Australia
cane toads 399
climate 245, 265
continental drift 215
marsupials 335
winds 254
autopilots 119
avalanches 266
avocets 333
Avogadro, Amedeo 51
Avogadro’s Law 51, 404
axles 131
axolotls 328, 329
aye-ayes 336
Ayers Rock 230
azimuthal projection, maps
240

Aztecs 241

Babbage, Charles 172,174
babies, growth and
development 363, 368
baboons 336
Bacon, Francis 49
bacteria 305, 313
antiseptics 105
cells 339

deep-sea 234, 386
diseases 351
drugs 104, 105
lifespans 422
nitrogen cycle 373
sulphur 45
viruses and 312
yoghurt 80
Baekeland, Leo 100
Baikal, Lake 388
Baird, John Logie 167
Bakelite 100
balanced forces 117
ballbearings 121
balloons
air inside 50
helium 48, 129
hydrogen 47
weather forecasting 271

434

INDEX

balls, motion 119, 120
bananas 366
banks, computers 175
bar codes, laser readers
199

bar magnets 154
barchan dunes 231
barium 63
barium sulphate 35
barnacles 357, 385
barometers 127,250
Barringer meteorite 295
basalt 217, 222
basaltic volcanoes 217
bases 70 - 1 , 73
Bates, Henry 305, 380
batfishes 327
batholiths 222
bats 334
evolution 308
roosts 397
sounds 183
batteries 150-1
alkaline 70
dry-cell 139
electricity 148
lead-acid 68
zinc 36

bauxite 87, 407
Bayer process 87
beaches 236, 237, 385
beaks, birds 333
beam bridges 117
bears

hibernation 381
nutrition 342
polar 382, 400
Beaufort, Admiral Sir
Francis 256
Beaufort scale 256
Becquerel, Antoine 26
bedding planes 223
Bednorz, Georg 149
bees

communication 351,378
nests 397

pollination of flowers
319, 380
beetles 311,352
Bell, Alexander Graham
163, 181
beluga 382
benzene 41,96
bergschrunds 228
Bernard, Claude 351
Bernoulli’s Principle 128
Berzelius, Jons 41, 53, 56
Bessemer, Henry 84
beta rays 26
bi-metallic strips 141
bicarbonate of soda 69,71
bicycles
dynamos 159
friction 121
pumps 19, 51
Big Bang 17,31,275,296
bile 76

binary stars 279
binary system 172, 174,

411 '

binders, paints 102
binocular vision 359
binoculars 198
biodegradability 101, 376
biology seeanimals; living
things; plants
biomass energy 134
biomes 370
biosphere 370-1
cycles 372-3
biotechnology 93
birds 332-3
brains 361
classification 421
colonies 378

colour 380

endangered species 398
evolution 227, 308, 309
flight 128,357
gliding on thermals 262
lifespans 422
partnerships 379
in polar lands 382-3
in rainforests 394-5
reproduction 367
on seashores 385
in towns and cities 397
in wetlands 389
birds of Paradise 395
Birdseye, Clarence 93
bison 393, 400
bitumen 98
bituminous coal 238
bivalves 324
Black, Joseph 74
black dwarf stars 281,285
black holes 281
blastfurnaces 84
bleaching 65
blinking 356
block mountains 218
blood 348, 350
circulation 349
functions 351
haemoglobin 77
bloodworms 375
blue light 202
skies 200, 269
bluebottles 307
boa constrictors 330, 394
body see animals; human
body

body temperature 423
bogs 238, 389
Bohr, Niels 25
boiling point 20, 23, 140-1
bolas spiders 322
Boltzmann, Ludwig 50
bomb disposal robots 176
bombadier beetles 323
bombs, nuclear 137
bonding 28-9, 52
bones

calcium 35, 43
fossils 225

weather folklore 272
see also skeletons
bongos 380
boomerangs 122
boron 39
Bosch, Carl 90
bottles, glass 110
bower birds 361
Boyle, Robert 49
discovers phosphorus 43
theory of acids 69
theory of sound 177
Boyle’s Law 51, 404
Bragg, William Henry 30
Bragg, William Lawrence 30
Brahe, Tycho 296
brains 361

control of muscles 355
monitoring body 350
nervous system 360
senses 358
vision 204
brakes 19,121,128
braking distance 119
Brand, Hennig 31, 43
brass 88

brass musical instruments
187

bread 80, 93
breast-feeding 368
breathalysers 65
breathing 347
breezes 255
bricks 109
bridges 117,141

bristlecone pines 246, 317
brittleness 23
broadleaved trees 396
Brocken spectres 269
bromeliads 394
bromine 46, 50
bronze 38, 88
Brown, Robert 50
Brownian motion 50
brushes, electric motors
158

bryozoans 320, 421
bubble chambers 17
bubbles 128,202
bubonic plague 313
“buckyballs” 40
buffers 72

Buffon, Georges-Louis
308

buildings
earthquakes 220
electricity supply 161
energy 135
forces 113, 117
fungi in 315
insulation 142
lightning conductors 147
stone 223
weather and 245
bulbs 366
bullfrogs 328
bumblebees 319, 380
buoys, weather 271
burglar alarms 155
Burnell, Jocelyn 281
burning 44, 64-5
burrowing animals 393
bush fires 265
bushbabies 336
butane

covalent bonds 29
liquid gas 97
molecular structure 41
oil products 98
butterflies
camouflage 380
caterpillars 363
conservation 400
buttresses, cathedrals 117

cables

electricity supply 160
fibreoptic 162, 177
cacti 390, 391
caddisflies 343
caecilians 328, 329
caesium 34
caimans 331,388
calcite 221, 231
calcium 35
Periodic Table 32
reactivity 405
calcium carbonate
in glass 110
in hard water 75
in skeletons 352
uses 70

calculators 145, 172 , 191
calendars 273, 282
Callisto 290

Cambrian period 227, 229
camels 342, 390
camera obscuras 206
cameras

cinema 177, 208
photography 206
television 166, 177
camouflage 380
cancer 27, 105
cane toads 399
canine teeth 344
canned food 92, 93

Cannon, Annie Jump 278
capacitors 147, 168-9
capillaries 349
capillary action 128
Capitol, Washington 84
caramel 79

carbohydrates 79, 342, 345
carbolic acid 96, 105
carbon 40

alkanes and alkenes 406
atoms 24

carbon cycle 41,372
coal 238

iron and steel 84-5
in living things 305
metal alloys 88
oil 98-9

organic chemistry 41
Periodic Table 33
carbon dating 27
carbon dioxide 40
acid rain 231
in air 7 4

air-conditioning 70
carbon cycle 372
dry ice 20
fossil fuels 135
greenhouse effect 40,

247, 372
identifying 404
photosynthesis 65, 340
rainforests 395
carbon fibres 40
carbon monoxide 24
carbonates 69
Carboniferous period 227,
229, 238
carnivores
feeding 342, 343
teeth 334, 344
carrier signal 164,165
cars

acceleration 119
batteries 151
battery-powered 151
brakes 19,128
catalytic converters 57
driving in fog 263
driving mirrors 195
engines 65, 143
fuel gauges 157
hydrogen-fuelled 47
metals 36
robots 176
speed 118

stopping distance 119
cartilage 353
cartilaginous fish 326,

357, 421

cartography 240
cassette tapes 155
catabolism 76
catalysts 56-7
adhesives 106
cracking oil 99
catalytic converters 57
caterpillars 342, 363, 380
cathedrals, flying
buttresses 117
cathodes 67, 168
cats

genetics 365
senses 358
skins 399

Cavendish, Henry 47, 123

caves 228, 236

cavies 393

CD players 171

CD-ROMs, computers 173

celery 341

cells

bacteria 313
blood 348
brain 361
electricity 150-1

genetics 364-5
growth 362-3, 365
living things 337,

338-9

protists 314
respiration 346
sexual reproduction 367,
368

cellular networks,
portable telephones 163
celluloid 100
cellulose 339, 345, 352
Celsius, Anders 140
Celsius scale 140
cement 109
centigrade 408
centipedes 322, 396
classification 421
exoskeleton 352
central processing units
(CPU) 172,174
centre of gravity 122, 124
centrifugal force 125, 211
centrifuges 61
centripetal force 125
cephalopods 324
Cepheid stars 279,281
ceramics 109
Ceres 294
cermets 111

Cerro Tololo observatory
297

cetaceans 334
CFCs (chlorofluorocarbons)
ozone destruction 57,

112, 375
uses 46

Chadwick, James 25
chaffinches 333
Chain, Ernst 105
chalcopyrite 86
chalk

chemical name 53
formation of 314
hot springs 35
properties 23
soils 232
chameleons 203
Channel Tunnel 179,199
Chaptal, Jean Antoine 89
charcoal 40

Chardonnet, Count Hilaire
107

charged particles 213
Charles’ Law 51, 404
Charon 293
charts, weather 270
Chatton, Edouard 338
cheese 80, 92, 315
cheetahs 356, 392
chelonians 331
chemical analysis 62-3
chemical change 49
chemical energy 133, 138
chemical industry 82
chemical reactions 52
chemical weathering 230
chemistry
alchemy 17
in farming 91
in medicine 104-5
see also individual
chemicals

Cherenkov, Pavel 26
Chernobyl nuclear power
station 27, 137
cherry trees 318, 342
chicken-pox 312
Chile pine 317
chilopoda 322
chimpanzees 336, 378
China 108,256,270
Chinook wind 254
chips see integrated
circuits

435

INDEX

Chiron 294
chitin 352
chlorine

alkali industry 94
Avogadro’s Law 51
chlorinating water 46
Periodic Table 33
see also CFCs
chlorophyll
chloroplasts 339
magnesium and 35
iron and 36
photosynthesis 316, 340
chloroplasts 339, 340
chordates 421
Christmas 243
chroma, colour 203
chromatography 62
chromosomes 362, 364-5
chromosphere 284
chrysalises 363
chuckwallas 390
cinema 208
circuits 152-3
circuit boards 149,170
circuit breakers 161
integrated 170-1
magnetic 155
circular motion 125
cirrus clouds 249, 260-1
cities (ecology) 397
climate 417
ecosystems 371
microclimate 244
smog 263
citric acid 68, 73
clams 205, 324
classifying living things
310-11, 420-1
clay

pottery 109
soils 228,232
terracotta 81
cliffs 314
climate 241
and animals 142
cities 417
deserts 390-1
grasslands 392
ice ages 229
polar and tundra lands
382

rainforests 394
seasons 211
and soil formation 232
temperate forests 396
climates 244-5
changing 246-7
see also weather
climax community 371
climbing plants 359, 394
dints 231
clocks
atomic 34
chemical 54
pendulums 126
sundials 201
clones 366
clothes
cleaning 95
fibres 81, 107
clots, blood 348
clouds 249, 260-1
fog, mist and smog 263
formation of 262
fronts 253
hail 267
lightning 147
rain 241,264
“seeding” 265
snow 266

thunder and lightning
257

weather forecasting 270,
271

clusters
galaxies 276
stars 280

cnidarians 320, 421
coal 238
carbon 40
explosions 55
formation 223, 225
historical geology 226
mining 238
power stations 135
products 96
reserves of 135
smog 263
uses 407
coal tar 96
coastlines 236-7
cobalt 32
cobras 330
cochlea 182, 358
cockchafers 359
Cockcroft, John 25
Cockerell, Christopher 121
cockroaches 356, 363
codes
binary 411
Morse 162, 411
coelacanths 234
cohesion 128
coils

electric motors 158
electromagnetism 156,

157

coke 84, 96
cold-blooded creatures
326,350, 423
cold fronts 253, 270
cold packs 52
colds 312
collision theory 55
colonies, birds 378
colour 202
chemical clocks 54
cosmetics 103
crystals 30

dyes and pigments 102
flame test 63
food colourings 93
genetics and 365
light 193

in living creatures 380
minerals 221
photography 207
rainbows 269
skin 354
•sky 200, 269
subtraction 203
television 166, 167
and temperature 140
vision 205

colour blindness 205
Columbus, Christopher 215
combine harvesters 130
combining forces 116
combustion 65
comets 283, 295
commensalism 379
communications
pheromones 351
radio 164-5
sound and light 177
speech 182

telecommunications 162-3
television 166-7
commutators 158
compact discs (CDs) 39,

188

compasses 145, 154
compost heaps 376
compound eyes 205
compound microscopes 198
compounds 53, 58-9, 67
computers 173-4
astronomy 296
calculators 172

computer-aided design
(CAD) 175
discs 155

electronic sound 189
integrated circuits 170
robots 176

speech recognition 183
telecommunications 162
using 145, 175
weather forecasting 271
concave lenses 197,204
concave mirrors 195
concentration, rate of
reactions 55
Conception 250, 251
condensation
changes of state 20-1
clouds 262
dew 268

fog, mist and smog 263
polymers 100
conduction 142
conductivity 23
conductors
copper 86
electricity 148
metals 29
properties 22
superconductors 149
cone shells 324
cones, vision 205
conglomerate 223
conical projection, maps
240

conifers 317
classification 420
forests 396
lifespans 422
on mountains 384
conservation 400
energy 139

constellations 282, 419
consumers, food chains 377
contact forces 115
contact lenses 204
continental climate 244
continental crust 210
continental drift 214
continental shelf 234, 387
continents
formation 210
mountain building 218
plate tectonics 214-15
contrails 261
convection 142
convection currents 142,
255

convergent evolution 390
convex lenses 197,204
convex mirrors 195
cookery 78

Copernicus, Nicolas 287
copper 86
bronze 88
conductors 148
electrorefining 67
flame test 63
Periodic Table 32
reactivity 66, 403
salts 73
uses 407
copper oxide 73
copper sulphate 73, 75, 86
coprolites 225
corals 320
reefs 223, 234, 387
core, Earth 212,213
cornea 204
corona, Sun 284
corundum 221
cosmetics 103
Cosmic Background
Explorer (COBE) 275
cosmology 274
cotton 107

cotyledons 318,362
Coulomb, Charles Augustin
149

counting, binary system
172, 174, 411
courtship 329, 367
Cousteau, Jacques-Yves 387
covalent bonds 28, 29
cows 272, 345
Coxwell, Henry 249
coypus 344

Crab Nebula 281,297,298
crabs 322
blood 348
larvae 363

sea anemones and 379
on seashores 385
shells 352

cracking, oil 57, 99, 406
craneflies 357
craters
Mercury 286
meteorite 295
moon 287
creosote 96
creosote bushes 391
Cretaceous period 227,

229,239

crevasses, glaciers 228
(Tick, Francis 364
crocodiles 331, 344
crocuses 1 40
Croll,James 246
cross-pollination 367
crossbills 396
crust, Earth’s 210, 212,

214

crustaceans 322, 348, 421
crystal sets, radio 164
crystals 30
ionic structure 28
minerals 221
salts 73

snowflakes 266
water of crystallization
75

cuckoos 333
cucumbers 318
cumulonimbus clouds 261,
264, 267

cumulus clouds 260-1
Curie, Marie 26, 35
Curie, Pierre 26
current electricity 148-9
alternating 159, 160
direct 159, 160
current marks
geology 226

currents, ocean 235, 244
cuttlefish
ink 102

skin colour 203, 354
swimming 357
cyanobacteria 307
cyclones 258
cylindrical projection,
maps 240
cypress trees 389
cytoplasm 338

Daguerre, Louis 207
Daimler, Gottlieb 144
daisies 318, 356
Dalton,John 24, 53
dams 388

darkrooms, photography
207

Darwin, Charles 309, 369
dating

carbon dating 27
fossils 225
geological time 227

Davy, Humphry
discoveries 67
electrolysis 34
miner’s safety lamp 238
day, length 211
deafness 181,182
decanting 61
decibel scale 181
deciduous forests 384
decimal numbers 411
decomposition
animals 376
molecules 59
recycling 372, 393
dedicated computers 170,
175

deep-sea fish 327
dehydrating agents 69
deltas, rivers 233
Democritus 24
dendroclimatology 246
density

floating and sinking 129
matter 22
dentists 88

depressions, weather 253,
270

Derham, William 179
dermis 354
desalination 83
desertification 247, 391
deserts (ecology) 371, 390-1
climate 241,245,390-1
erosion 230
humidity 252
rainfall 264, 265
sand 226, 231
spread of 247,391
desiccation 61
design, computer-aided
(CAD) 175

desk-top publishing 173
destructive testing 62
detergents 95
deuterium 136, 137
Devonian period 227, 229,
239

dew 262, 268
dew point 268
dew ponds 268
Dewar, James 142
diabetes 105
diamonds 40, 221
diaphragm 347
diatoms 352
dibromoethane 99
dicotyledons 318, 420
diet 342
see also food
diffraction, light 191
diffuse reflection 194
diffusion, gases 50
digestion 76, 345, 356
digital audio tape (DAT)

188

digital signals
electronic sounds 189
integrated circuits 171
sound recording 188
digitoxin 104
dik-diks 392

dimmers, light bulbs 153
dinosaurs 275, 330
evolution 308
extinction 227,331
fossils 225, 226
names 311
diodes 168-9
diploid cells 365
diplopoda 322
direct current 159, 160
generators 159
diseases
bacteria 313
body’s defences 351

436

INDEX

deficiency diseases 342
drugs 104-5
viruses 312

disks, computer 173,174
displacement reaction 66
distillation 61
see also fractional
distillation
divers, pressure 127
DNA (deoxyribonucleic
acid) 338
cell division 362
forensic science 62
genetics 337, 364-5
phosphates 43
viruses 312
the Doctor (wind) 254
dodder 379
dogfish 326, 357
dogs
fleas 379
hearing 183
senses 358, 359
teeth 334, 344
doldrums 254
dolphins 185,334
Domagk, Gerhard 105
domains, magnets 155
door latches,
electromagnetic 156
doorbells 156
Doppler effect 180
dormice 381
drag

aircraft 114
friction 123
rock faults 219
streamlining 121
drag racing 119
dragonflies
larvae 344,388
life cycle 323, 363
dreikanters 230
drift mines 238
drizzle 264
droughts 265
cycles 242
longest 416
lungfish 381
drugs 104-5
drums 187
dry cells 150-1
dry ice 20
ducks 332, 382-3
ductility 23
dunes, sand 231,237
dung, fossils 225
Dust Bowl 265
dyes 102
aniline 41,96
dykes, granite 222
dynamos 159

eagles 394
ears

hearing 182, 358
protectors 181
Earth 209,287
air pressure 250
atmosphere 74, 248-9, 287
biosphere 370-3
climate change 246
climates 242, 244-5
earthquakes 220
energy sources 134
fact finder 414-15
formation of 210-11,

275, 283

geological timescale
227, 414

global warming 247, 372
gravity 122, 125

how life began 307
hydrogen 47
ice and glaciers 228-9
magnetic field 115, 145,
154,213,215
mapping 240
mass 123

mountain building 218-19
plate tectonics 214-15
pollution 374-5
rivers 233

rocks and minerals 221-7
satellites 300
seas and oceans 234-7
seasons 243
shape 211
soils 232
statistics 418
structure 212 - 13 , 414
andtheSun 285
temperature 251-2
volcanoes 216-17
weathering and erosion
230-1

see also ozone layer
Earth Summit 400
earthquakes 220
seismic waves 178
tsunamis 235
vibrations 126,212
earthworms 321,352, 360
Eastman, George 207
echinoderms 325, 421
echo-sounding 185
echoes 184
eclipses 201,285
eclipsing binary stars 279
ecology 369
animal groups 378
biosphere 370-3
colour and camouflage
380

conservation 400
deserts 390-1
fact finder 424-5
food chains and webs 377
grasslands 392-3
migration and
hibernation 381
mountains 384
oceans 386-7
partnerships 379
polar and tundra lands
382-3

pollution 374-5
rivers and lakes 388
seashores 385
temperate forests 396
tropical rainforests 394-5
towns and cities 397
wastes and recycling 376
wetlands 389
wildlife in danger 398-9
ecosystems 370-1
Eddington, Sir Arthur 285
Edison, Thomas
cinema 208
electricity 160
light bulbs 193
sound recordings 188
eels 151,327
efficiency 130, 139
eggs

birds 332, 333
cells 338,365
frogs and toads 328
human reproduction 368
monotremes 335
reptiles 330, 331
sexual reproduction 367
Egypt

astronomy 296
cosmetics 103
River Nile 388
Ehrlich, Paul 104

eiderduck 382, 383
Einstein, Albert 118
Brownian motion 50
colour of sky 269
nuclear energy 136,137
theories of light 191,

199

theory of relativity
281,285
elasticity
force 115

potential energy 133,

138

properties of matter 23
electricity 113, 115, 145
cells and batteries 150-1
chemical reactions 52
circuits 152-3
conductors 23, 29
copper 86
current 148-9
electrolysis 67
electromagnetism 156-7
energy 133
factfinder 410-11
fish’s senses 359
generators 159
in the home 161
hydroelectric power 134,
233

lightning 257
motors 158
muscles 355
photoelectric effect 191
piezoelectricity 126
potential energy 133
power stations 135
semiconductors 149
solar power 134, 190
static electricity 115,

146 - 7 , 257

superconductors 149
supply 160
symbols 411
telecommunications
162-3

transmission lines 38
wind power 134, 255, 256
see also batteries
electrolysis 67
aluminium production 87
copper production 86
sodium hydroxide 94
electrolytes 68
electromagnetism 156-7
electromagnets 36
induction 159
spectrum 192 , 412
electromotive force
(e.m.f.) 150-1

electron guns, television 167
electron microscopes 339
electronics 145
calculators 172
components 168-9
computers 173-5
integrated circuits 170-1
robots 176
semiconductors 39
sounds 189
symbols 411
electrons
atoms 24-5
bonding 28-9
compounds 59
matter 18

oxidation and reduction
64

Periodic Table 33
photoelectric effect 191
static electricity 146
electroplating 67, 149
electrorefining 67
electroscopes 146
electroweak force 115

elements 31

compounds and mixtures
58-9

Periodic Table 32-3, 402-3
elliptical galaxies 276
embryo 368
emulsifiers 93
emulsions 59, 103
endangered species 398-9,
425

endocrine system 351
endoplasmic reticulum (ER)
338

endoscopes 196
endoskeletons 353
endosperm 362
endothermic creatures 332,
350, 423

endothermic reactions 52
energy 113 , 132-3
anabolic reactions 76
catabolic reactions 76
cellular respiration 346
chemical 52, 133, 138
coal 96,238
conservation 139
conversion 138-9
daily use by people 408
efficiency 139
electromagnetic spectrum
192

engines 143-4
fact finder 408-9
food chains and webs 377
heat 140-1
kinetic 133,138
living things 306
measuring 132
metabolic rate 423
nuclear 136-7
oil and gas 239
photosynthesis 340
potential 133, 138
sources of 134 - 5 , 409
stars 278
stored 133

wind strength 255, 256
work 132-3
see also electricity;
light; sound
engines 143-4
internal combustion 65
jet aircraft 88, 144
enlarging photographs 207
environment see ecology
enzymes

in the body 76, 77
catalysts 56, 57
digestion 345
washing powder 95
Eocene period 229
epicentre, earthquakes 220
epidermis 354
epoxy resin 106
equations
chemical 53
electricity 410
physics 408
wave 412
Equator
climate 244
doldrums 254
ocean currents 235
shape of Earth 211
temperature 251
equilibrium 117
reactions 54
stability 124
turning forces 124
erosion 230-1
glaciers 228
mountain building 218
rivers 233, 388
sedimentary rocks 223
shoreline 236

erratic rocks 228
escape velocity 299
estuaries 236, 385
ethane 97-8, 406
ethanoic acid 99
ethanol 99, 406
ethene

molecular structure 41
production of 97
uses 99, 406
Europa 290, 301
Europe
droughts 265
Ice Age 246

“Little Ice Age” 242, 246
temperate forests 396
European Space Agency
299

eutrophication 373
evaporation
air-conditioning 141
changes of state 20, 21
uses 61

Everglades 389
Everson, Carrie 86
evolution 308-9
convergent 390
genetics 364

exchanges, telephone 163
excretion 350
exoskeletons 352
exosphere 248
exothermic creatures 326,
350, 423

exothermic reactions 52
expansion 50
explosions 55
explosives 42
energy 138
gunpowder 65
shockwaves 181
exposure, photography 412
extinction 395, 398-9, 425
extrusion, plastics 101
eyes

blinking 356
lenses 197
rod cells 338
surgery 157
vision 204-5, 358-9

Fabre,Jean-Henri 323
fabrics
cleaning 95
dyes 102
fibres 81

faces, expressions 356
Fahrenheit, Gabriel Daniel
140

Fahrenheit scale 140,40#
fallout, radioactive 27
fanworms 343
Faraday, Michael 67,159
farming
chemistry in 91
droughts 265
humidity 252
irrigation 233
propagation 366
weather and 241
fats

chemistry 78
digestion 345
nutrition 342
faults, mountain formation
218,219

fax machines 163
feathers 332
feeding 343
digestion 345
teeth and jaws 344
see also food

437

INDEX

feldspar 39,221,231
fennec foxes 142, 390
fermentation 80
Fermi, Enrico 137
ferns 316, 420
fertilization 318-19, 367
fertilizers
ammonia 90, 96
eutrophication 373
farming 91
nitrogen 42
phosphorus 43
Fessenden, Reginald 164
fibreglass 111
fibreoptic cables 162,177
fibres 107
paper 108

filaments, light bulbs
161,193
films

cinema 208
photography 206-7
filters, light 202
filtration 61
finches 309,333
fingerprints 354
fins, fish 327
fir trees 317
fire

bush fires 265
fire-fighting 64, 71
oxygen and 44
phlogiston theory 64
fireworks 35, 63, 138
firn 228
fish 326-7
“antifreeze” 268
blood circulation 349
breathing 347
cartilaginous 326, 357,

421

classification 421
deep-sea 386
fishing 387

internal environment 350
lateral line 358
lifespans 422
migration 381
partnerships 379
reproduction 367
scales 354
senses 359
streamlining 121
swim bladders 129
swimming 357
fission, nuclear 136
Fizeau, Hippolyte 191
fjords 236
flame tests 63
flamingoes 333
flatworms 360, 421
flavourings, food 93
fleas 379

bubonic plague 313
evolution 309
jumping 356
Fleming, Sir Alexander
105,315

Fleming’s left-hand rule

158

Fleming’s right-hand rule

159
flies

eggs 307
eyes 205
wings 357
flight

aerofoils 128
birds 128,357
forces 114
simulators 175
float glass 110
floating 129
floodplains 233
flood's 233, 247, 264

Florey, Howard 105
Florida
coastline 247
Everglades 389
hurricanes 258
flowers 318 - 19 , 420
ultraviolet pigmentation
205

see also plants
fluids, forces in 128
see also gases; liquids
fluorescence 200
fluorescent lights 201
fluorides 46
fluorite 46, 73, 221
fly agaric 315
flying see flight
flying buttresses 117
flying fish 327
flying frogs 328
foetus 368
fog 261, 263
Fihnwind 254
fold mountains 218-19
folklore, weather 272
food

additives 93
antioxidants 65
astronauts 303
chemistry of 78-9
digestion 356
energy 132, 138
farming 91
feeding 343
fermentation 80
food industry 92-3
metabolic rate 423
nutrition 342
plants 341

preserving 69, 79, 92
food chains 377
grass 392
in oceans 386
in rivers 388
food poisoning 79
food webs 377
fool’s gold 62
footprints, fossil 225
foraminiferans 314
force fields 114
forces 113
acceleration 119
balanced 117
circular motion 125
combining 116
fact finder 408-9
floating and sinking 129
in fluids 128
friction 121
gravity 122
machines 130-1
measuring 123
and motion 120
pressure 127
speed 118
turning 124
vibrations 126
work 132

forecasting, weather 270-1
forensic science 62
forests

coal formation 238
coniferous 384
deciduous 384
temperate 371
see also tropical rainforests;
trees

fork lightning 257
formic acid 68
formulae, chemical 53
fossil fuels 135
fossils 225
amphibians 328
continental drift 215
and evolution 308

historical geology 226
prehistoric man 336
four-colour printing 203
four-stroke engines 143
Fox-Talbot, William 207
foxes 379, 397
foxgloves 319,380
fractional distillation
74, 98-9

Franklin, Benjamin 147
Franklin, Rosalind 364
Frasch process 45
Fraunhofer lines 193
Freedom space station 304
freezing

changes of state 20
food 92, 93
ice 75
frequency
music 187, 413
sound waves 180
vibrations 126
frequency modulation (FM)
164

Fresnel, Augustin 197
Fresnel lenses 197
friction 121
air resistance 119, 121
machines 130
static electricity 146
frogs 328

blood circulation 349
brains 361
muscles 355
rainforests 394
sounds 183

fronts, weather 253, 270
frost 231,268
fruit, browning 79
fuel

engines 143
fossil fuels 135
rockets 299
fuel cells, catalysts 56
fuel gauges, cars 157
Fuji, Mount 217
fulcrum 124, 131
fungi 315

classification 311, 420
feeding 343
lifespans 422
rainforests 394
fungicides 91
fur trade 399
furnaces, iron industry 84
fuses 152, 161
fusion see nuclear fusion

Gagarin, Yuri 302
Gaia theory 370
Galapagos Islands 309, 330
galaxies 274, 276-7
gales 256
Galileo Galilei 127
observations of planets
286, 290, 291
pendulum clock 126
telescope 273, 297
theory of motion 120
Galileo space probe 301
asteroids 294
batteries 37
andjupiter 290
gall wasps 396
Galle,Johann 292
Galvani, Luigi 355
galvanizing 66
gametes 364-5, 367
gamma rays
astronomy 298
electromagnetic spectrum
192

radioactivity 26, 27
Universe 277
Gamow, George 275
Ganymede 290
garpike 389
gas 239
coal 96
products 97
reserves of 135
uses 407
gas oil 98
gases 18-19
behaviour of 51
changes of state 20
chromatography 62
collecting 404
compressed 19
density 22
expansion 141
forces 128
heat transfer 142
identifying 404
kinetic theory 50
and light 193
noble 48
pressure 127
reactions 404
solutions 60
speed of sound 179
stars 278, 280
temperature 141
gasoline 98
Gaspra 294
gastropods 310, 324
gavials 331

Gay-Lussac, Joseph Louis

Gay-Lussac’s Law 51, 404
gazelles 343, 392
gears 131
geckos 330, 395
geese 400
Geiger counters 27
Gell-Mann, Murray 25
generators 145, 159, 160
genes 364-5, 367
genetics 337, 364-5
asexual reproduction 366
genetic fingerprinting
62

sexual reproduction 367
genus 310
geodes 221

geological time 227, 414
geology 209
see also rocks
geomorphology 209
geostationary orbits,
satellites 300
geothermal energy 134
germanium 33
germs see bacteria; viruses
gestation periods 422
geysers 134,217
gibbons 337
gila monsters 390
Gilbert, William 145, 213
gills 327, 347, 349
Giotto space probe 295
giraffes 379, 392
gizzards 332
glaciers 228-9
fjords 236
snow 266

Glaisher, James 249
glands, hormones 351
Glashow, Sheldon 115
glass 110
boron 39
glass-reinf orced
plastics 111
lead crystal glass 38
lenses 197
manufacture 406
photochromic 200

gliding, birds 357
global warming 247, 372
glucagon 351
glucose

cellular respiration 346
chemical formula 79
digestion 345
hormone control 351
in the liver 76, 77
photosynthesis 340
glues 106
glutamic acid 307
gneiss 224
Gobi desert 390, 391
Goddard, Robert 144,

299

gold 31, 36-7
copper by-product 86
purity 59
reactivity 66, 405
testing 62
Gondwana 215
Goodall,Jane 378
goose pimples 350
Gould, Gordon 199
Graham’s Law of Diffusion
404

Grand Canyon 226
Grand Unified Theory
(GUT) 115
granite 221
formation 222
mountain building 218
weathering 231
graphite 40
grasses

cow’s digestion 345
pollination 318
grasshoppers
camouflage 380
ears 358

metamorphosis 363
nerves 360
sounds 183

grasslands (ecology) 371,

392-3

Alpine 384
gravity 115, 122
air pressure 250
centripetal force 125
escape velocity 299
galaxies 275, 276
microgravity 304
potential energy 133
Solar System 283
stability 124
stars 280

terminal velocity 119
theory of relativity 281
weightlessness 303
grease, soaps and
detergents 95
Great Barrier Reef 387
grebes 367
green light 202
greenhouse effect 40, 247,
372

Greenland
glaciers 228
ice sheets 229, 246
snow 266

grid system, electricity
supply 160
grikes 231

growth and development

362-3

groynes 237
guinea pigs 393
guitars, electric 189
Gulf Stream 235
gunpowder 65
guttation 341
gypsum 73
crystals 30
Mohs’ scale 221, 415

438

INDEX

gyres 235
gyroscopes 125

Haber, Fritz 90
habitat 370
Haeckel, Ernst 369
haemoglobin 77, 348
Hahn, Otto 137
hail 257, 264, 267
hair 354

Hale Reflector 198
half-life, radioactivity
26

Hall, Charles Martin 87
Halley, Edmond 295
Halley’s Comet 295, 297,
301

haloes, Sun and Moon 260,
269

halogens 46
hammer throwers 125
hanging valleys 228
haploid cells 365
hard water 75
hardness, Mohs’ scale 221,
415

hardware, computers 173,
174

harmonics 186
harmony 186
Harvey, William 349
Hawaii 217,264
Hawaiian geese 400
Hawking, Stephen 189
head and tail dunes 231
headlands, erosion 236
hearing 181-2, 358
hearing aids 182
heart 349, 355
heat 140-1

chemical reactions 52
conductivity 23
conservation 112
transfer 142
work and 132
“heat islands” 244
heat resistant materials
111

heath fritillaries 400
Helin, Eleanor 294
helium 48, 137
balloons 18, 129
on Jupiter 290
production of 97
in stars 278, 280
in the Sun 284, 285
in the Universe 31, 275
hematite 221
Henry,Joseph 158
herbicides 91, 373
herbivores
feeding 342, 343
teeth 334, 344
herd animals 343
hermit crabs 379
Her.ult, F.L.T. 87
herpes viruses 312
herrings 387
Herschel, William 198,

277, 292

Hertz, Heinrich 164, 180,
192

Hertzsprung, Enjar 279
Hertzsprung-Russell
diagram 279
heterogenous theory,
formation of Earth 210
Hewish, Tony 281
hibernation 381
Himalayas 218,384
Hindus 209
Hippocrates 104

Hiroshima 137
historical geology 226-7
HIV 312
hoar frost 268
I Ioffman, Felix 104
Hollerith, Herman 174
Hollywood films 208
holograms 199
homeostasis 350
Homo sapiens 336
homogenous theory,
formation of Earth 210
honeybees 351, 378
honey f ungus 396
honey possums 319
honeydew 341
Hooke, Robert 123, 338
Hooke’s law 123
hormones 350, 351, 363
horologium 255
horses 308, 400
horsetails 420

hot spots, Earth’s mantle 217
hot springs 18
chalky “icicles” 35
geothermal energy 134
geysers 217
house dust mites 354
house martins 397
houses s^buildings
hovercraft 121
hoverflies 380
Howard, Luke 260
howler monkeys 183
Hubble, Edwin 274, 276
Hubble Space Telescope
298, 300

Hubble’s law 274
hue, colour 203
Huggins, William 278,296
human beings
environment 369
evolution 308, 336
pollution 374-5
population growth 373,

424

towns and cities 397
human body
artificial parts 111
blood 348

blood circulation 349
brain 361
breathing 347
cellular respiration 346
chemistry of 76-7
digestion 345
ears 182
eyes 204-5
feeding 343
genetics 364-5
growth and development
362-3

internal environment
350-1

medicine 104-5
movement 356
muscles 355
nerves 360
reproduction 368
senses 358-9
skeleton 353
skin 354
speech 182
teeth and jaws 344
water content 75
weightlessness 303
humidity 75, 252 , 272
hummingbirds 342
humus 232
hunting 343, 392-3
Huntsman, Benjamin 81
hurricanes 256, 258
Hutton,James 226, 227
Huygens, Christiaan 190,

291

IIuysum,Jan van 312
Hyatt, John 100
hydra 366
hydraulics 19, 128
hydrocarbons
oil products 98-9, 239
cracking 99, 406
hydrochloric acid 68-9, 76
hydroelectric power 134,
233

hydrogen 47
acids 68-9, 72
alkanes and alkenes 406
ammonia 90
bombs 137
bonds 29

how life began 307
identifying 404
onjupiter 290
in natural gas 97
oxidation and reduction
64

in stars 278, 279, 280
in the Sun 284, 285
in the Universe 31, 275
water 75

hydrogenation 65
hydrometers 22
hydroxide ions 70
hyenas 392,393
hygrometers 252
hyphae 315
hypothalamus 351
Hymcotherium 308

Ibn Al-Nafis 349
ice 75, 228 - 9 , 268
changes of state 21
clouds 260
comets 295
frost 268
hailstones 267
polar lands 382
rain formation 264
snowflakes 266
temperature 140
Ice Ages 227
changing climate 246
glaciers 228-9
“Little Ice Age” 242, 246
raised beaches 237
ice caps 228-9
in Ice Age 246
on Mars 289
snow 266
icebergs 228-9, 263
Ichthyosaurus 225
icicles 268
ideal gas law 404
igloos 245

igneous rocks 221,222,
415

iguanas 330
illusions, optical 204
immiscible liquids 59
immune system 351
imperial measurements
409

Incas 243
incisor teeth 344
inclined planes 131
India

continental drift 215
monsoon 245, 264
Industrial Revolution 74,
238

industry
alkali 94
chemical 82
food 92-3
iron and steel 84-5
pollution 112

robots 176
water 83
inertia 120, 125
information
computers 173
telecommunications 162
infrared radiation (IR)
astronomy 298
Earth 248

electromagnetic spectrum
192

Sun 142,284
Universe 277
Ingenhousz, Jan 340
inheritance 365
insecticides 91, 323, 377
insects 323
breathing 347
classification 421
exoskeleton 352
eyes 205
flight 357
fossils 225
metamorphosis 363
mouthparts 344
nervous systems 360
pollination of flowers
318,319
senses 359
sounds 183
inselbergs 230
insoluble solids 60
instinct 361

insulation, heat loss 142
insulators
electricity 148
properties of matter 22,
23

insulin 105, 351
integrated circuits 170-1
calculators 172
computers 173
intelligence, computers
175

interference 191, 202
interferometry 297
internal combustion
engines 65, 143
internal environment,
human body 350-1
internal reflection 196
International Union for
the Conservation of
Nature and Natural
Resources (IUCN) 400
International Ultraviolet
Explorer (IUE) 298, 300
intestines 345
inversion, smog 263
invertebrates 320-5
classification 421
exoskeletons 352
Io 45, 290
iodine 32, 46
ionic bonds 28
ionosphere 165
ions

electricity 149
mass spectrometry 63
plasma 18
salts 73
solutions 60
iris, eyes 204
iron

compounds 58
discovery of 31, 66, 81
and steel 84-5
in living things 36
magnetism 154
reactivity 405
rust 44, 64
uses 407
iron ore 84, 221
irradiation, food 93
irregulargalaxies 276

irrigation 233
islands, coral reefs 234
isobars 250, 270
isomers 41
isotopes 24, 26-7
ivy 397

jacana birds 127
jack-rabbits 390
jackals 343
Jacobson’s organ 359
Jacquard, Joseph 174
jaguars 394
Janssen, Zacharias 338
Japan

cherry blossom 272
kites 256
weather 270
jaws 344
jellyfish 320
Jenner, Edward 105
jet aircraft
alloys 88
engines 144
sonic boom 177, 179
JET (Joint European Torus)
137

jet propulsion, squids 357
jet streams 254
Jewel Box cluster 279
jewellery 221
joints, bones 353
Joliot, Frederic 26
Joliot-Curie, Irene 26
Joule,James 132
joules 132

joysticks, computers 173
Jupiter 290
asteroid belt 294
formation of 283
moons 45, 273, 290, 301
space probes 273, 290, 301
statistics 418
Jurassic period 227, 229,
239

kame, glaciers 228
kangaroo rats 390
kangaroos 335
kaolin 109, 407
Keck telescope 198
kelp 316
Kelvin, Lord 138
Kelvin scale 138, 140, 408
Kenya, Mount 384
Kepler, Johannes 296
kerosene 98
kestrels 333
Kevlar 101

keyboards, computers 173,
174

keypads, calculators 172
kidneys 77, 350
kilns 64, 109
kilocalories 132
kilojoules 132
kinetic energy 133, 138
kinetic theory 50
kingfishers 332, 388
Kirchoff, Gustav 193
kit foxes 390
kites 256
kiwi fruit 318
kiwis 332
koalas 335, 400
Koch, Robert 313
Kodak 207
Kola peninsula 212
Komodo dragons 330

439

INDEX

Krebs, Hans 346
Krikalev, Sergei 303
krypton 48

Kwoleck, Stephanie 101

La Paz 250, 251
laboratories 49, 405
laccoliths 222
lactic acid 77, 346
Lactobacillus bulgaricus
339

ladybirds 380
Laika 300

lakes (ecology) 371, 388
acid rain 68, 71
ox-bow 233
lammergeyers 384
lampreys 326
Land, Edwin 207
land breezes 255
landslides 232
Lange\in, Paul 185
langurs 384
lanthanides 37
larches 317
larvae

caddisflies 343
crabs 363
dragonflies 344
lasers 190, 199
CD players 188
diode 39
refraction 196
wavelengths 202
latent heat 141
lateral line 358
Latin names 310
latitude 414
lattices 18
crystals 28, 30
Laurasia 215
Laurent, Auguste 69
lava

igneous rocks 222
volcanoes 140, 216, 217
Lavoisier, Antoine 17, 44,
64, 74

Lavoisier, Marie 17
Le Chatelier, Henri 54
Le Chatelier’s principle
54

Le Mans Cathedral 117
leaching, copper 86
lead 38
flame test 63
Periodic Table 33
pollution 112, 372
reactivity 405
lead-acid batteries 68,

151

Leakey family 336
learning 361
leaves

conifers 317
movement 356
photosynthesis 340
transpiration 341
Leclanche, Georges 150
LEDs (light-emitting
diodes) 151,169,193
leeches 321,388
Leeuwenhoek, Antoni van
197, 366

left-hand rule 158
legs 356
lemmings 383
lemon, electrical cell 151
lemurs 336
Lenoir, Etienne 144
lenses 197
cameras 206, 208
eyes 204, 358

spectacles 204
telescopes 297
Leonov, Aleksei 299
leopards 380, 384
leukaemia 105
levees 233
levers 130,131
Leyden jars 147
lichens 375, 383
life on Earth 287
wa/voanimals; living
things; plants
lifespans 422
lift, aircraft 114, 128
ligaments 353
light 177, 190-91
astronomy 298
atomic emission spectrum
63

chemical reactions 52
cinema 208
colour 202-3

electromagnetic spectrum
192

fact finder 412-13
lasers 199
lenses 197
and matter 200
optical instruments 198
photography 206-7
rainbows 269
rate of reactions 55
reflection 194-5
refraction 196, 413
shadows 201
sources of 193
spectrum 193, 202
speed of 118, 190-1,274
stars 279

theory of relativity
281, 285
vision 204-5
light bulbs 145,190
dimmers 153
electricity 161
energy efficiency 139
invention of 193
light emitting diodes
(LEDs) 151,169,193
light years 274
lightning 257
electrical reactions 52
energy conversion 138,
177

hailstones 267
static electricity 146-7, 249
lightning conductors 147
lignin 108, 352
lignite 238
lilies, brush 400
lime 70, 71
limestone 70, 73
erosion 231,232
formation 223
historical geology 226
iron industry 84
and marble 224
mountain building 219
pavements 231
limpets 324, 355, 385
Linnaeus 310
lions 392, 393
liquid, viscosity 19
liquid crystal displays
30, 140
liquids 18-19
changes of state 20-1
forces 128
heat transfer 142
hydraulic pressure 19
kinetic theory 50
mixtures 59
pressure 127
solutions 60
speed of sound 179

surface tension 128
temperature 141
Lister, Joseph 105
lithification 223
lithium 34, 63
Lithops aucampae 305
lithosphere 212, 214
litmus paper 72
“Little Ice Age” 242, 246
liver 76-7, 337, 350
liverworts 316, 420
living matter 17,41
living things 305
amphibians 328-9
arthropods 322-3
bacteria 313
birds 332-3

classifying 310-11, 420-1
evolution 308-9
fact finder 420-3
fish 326-7
fungi 315
how life began 307
how they work 337-68
jellyfish, anemones and
corals 320
mammals 334-5
molluscs 324
plants 316-19
primates 336
reptiles 330-1
single-celled organisms
314

starfish and sea squirts
325

viruses 312
what is life? 306
worms 321

see also animals; ecology;
human body; plants
lizards 330, 350
lobsters 322, 348
Local Group, galaxies 276
locomotion 356
lodestone 145
logic circuits 171
London, smog 263
long sight 204
longitude 414
longitudinal waves 1 78
longshore drift 237
Lorentz, Hendrik 194
loudness 181
loudspeakers 156, 183
magnets 37, 157
radio 165

Lovelock, James E. 370
Lowell, Percival 289
lubrication 19
lugworms 321,385
Lumiere brothers 208
Luna space probes 301
lungfish 381
lungs 347
birds 332

blood circulation 348
Lyell, Sir Charles 226
lymphatic system 351

McCandless, Bruce 302
Mach, Ernst 179
machines 130-1
electric motors 145, 158
perpetual motion 139
MachuPichu 243
mackerel sky 261
maggots 307, 375-6
magma 217,221-2
magnesium 35
Periodic Table 33
reactivity 405
magnesium hydroxide 70

magnetic levitation trains
156

magnetism 115, 145, 154-5
Earth’s magnetic field
115, 145, 154,213,215
electric motors 158
electromagnetism 156-7
factfinder 410-11
force fields 114
generators 159
loudspeakers 37
metals 36

potential energy 133
in rocks 215
magnetopause 213
magnetosphere 213
magnetotail 213
magnifying force 130, 131
magnifying glasses 197,198
magnitude, stars 282
Maiman, Theodore 199
main sequence stars 279,
280

malaria 314
malleability 23
malnutrition 342
mammals 334-5
classification 421
evolution 227, 308
gestation periods 422
hair 354
lifespans 422
metabolic rate 423
milk 368
primates 336
teeth 344

see also human body
man-o’-war 320
manatees 389
mangrove swamps 389,398
manned manoeuvring units
(MMUs) 302
mantle, Earth’s 212
hotspots 217
igneous rocks 222
plate tectonics 214
maps 209, 240
stars 282

weather 250, 253, 270,

416

mara 393
marble 224

Marconi, Guglielmo 164
mares’ tails (clouds) 261
margarine 65
Marianas Trench 386
Mariner space probes 286,
301

maritime climate 244
marmots 381
marram grass 385
marrow, bone 353
Mars 289
atmosphere 248
formation 283
space probes 176,289,

301

statistics 418
marshes 237, 389
marsupial mammals 335,
421

mass 22
energy and 136
and weight 122
mass spectrometry 63
matches 43, 52
materials 81-112
chemical industry 82
design 111
fact finder 406-7
recycling 112
see also individual materials
mating 367
matter 17
bonding 28-9

changes of state 20-1
crystals 30
elements 31
factfinder 402-3
light and 200
metals 34-9
Periodic Table 32-3
properties of 22-3
radioactivity 26-7
states of 18-19
Matthews, Drummond 214
Maunder, Edward 242
Maxwell,James Clerk
colour photography 207
electromagnetism 164,

192,194
meanders 233
measuring
forces 123
metric and imperial
measurements 409
sound 180

mechanical advantage 131
medicine 104-5
endoscopes 196
laser surgery 199
see also diseases
megalopa larvae 363
meiosis 362, 365, 367
Meitner, Lise 137
melanin 354

melting point 20, 23, 140-1
memoiy, computer 174, 175
Mendel, Gregor 365
Mendeleyev, Dimitri 32
meniscus 128
Mercalli scale 220
Mercator, Gerardus 240
Mercator projection 240
mercury

barometers 127, 250
meniscus 128
Periodic Table 32
poisoning 373
Mercury (planet) 286
formation 283
space probes 301
statistics 418
mercury oxide cells 150
Merychippus 308
Mesohippus 308
Mesosaurus braziliensis 215
mesosphere 248, 298
metabolism 76, 423
metal detectors 157
metals
alkali 33,34
alkaline-earth 35
alloys 59, 88
bonding 28, 29
conductivity 29, 142
electroplating 67
expansion 141
flame test 63
history 66
Periodic Table 33
poor 38

properties 22, 23
reactivity series 66
semimetals 39
transition 36
see also individual
metals

metamorphic rocks 224, 415
formation 221
oil production 239
metamorphosis 363
meteorites 295, 307, 418
meteoroids 287
meteorology see weather
meteors 121, 295
methane

chemical reactions 52
formation of 239
from rubbish tips 112

440

INDEX

gas products 97
how life began 307
oil products 98
methanoic acid 68
methanol 56, 93
methyl orange 72
metric measurements 409
mica 221,224
mice 306, 345
microbes
biotechnology 93
fermentation 80
in food 92

see also bacteria; viruses
microchips see integrated
circuits

microclimate 244
microgravity 304
microphones 180, 183
hearing aids 182
moving coil 159
parabolic dishes 184
radio 165
telephones 162
microscopes 123, 198
electron 339
lenses 197

light microscopes 339
polarized filters 221
microwaves

electromagnetic spectrum
192

ovens 139
telephones 163
MIDI (Musical Instrument
Digital Interface) 189
midnight Sun 243
migration 381, 425
milk

cheese 92

mammals 334-5, 368
pasteurization 92
Milky Way 274-7,280
Miller, Stanley 307
millibars 250
Millikan, Robert 25
millipedes 322, 421
mimicry 380
minerals
fertilizers 91
i n food 78
geology 209
Mohs’ scale 415
nutrition 342
rocks 221
in soil 232
mining, coal 238
Miocene period 229
Mir space station 300, 304
mirages 196, 269
Miranda 292
mirid bugs 363
mirrors
light 190

mirror images 194
telescopes 195, 198, 297
two-way 194
miscible liquids 59
mist 260, 263
mistletoe 318
mites 322,354
mitochondria 338, 346
mitosis 362
mixtures 58-9
separating 61
models, industrial plants
82

modems, computers 173
modulation, radio waves
164

Mohorovicic, Andrija 212
Mohorovicic discontinuity
212

Mohs, Friedrich 415
Mohs’ scale 221, 415

molar teeth 344
molecules 24
catalytic cracking 57
counting 53
covalent bonds 29
heat transfer 142
kinetic theory 50
polymers 41,100
solutions 60
temperature 140, 141
waves 178
moles 53, 335
molluscs 324
classification 310, 421
shells 306, 352
momentum 120
monerans 311, 340, 420
monitors, computers 174
monk seals 399
monkey puzzle trees 317
monkeys 336
in rainforests 394, 395
sounds 183

monocotyledons 318, 420
monotremes 335, 421
monsoon 245, 264
monsters, sea 259
months, length 287
Moog synthesizers 189
moon (Earth’s) 194, 288
ancient astronomy 296
astronauts 74, 299, 302
craters 273
eclipses 201,285
gravity 122
haloes 260, 269
space probes 288, 301
tides 235

moons 283, 287, 301
Jupiter 290, 301
Mars 289
Neptune 293
Pluto 293
Saturn 291
Uranus 292
moraine 228
morayeels 327
mordants, dyes 102
Morse, Samuel 162
Morse code 162, 411
mosquitoes 314
mosses 316, 420
moths 305
motion 120
circular 125
kinetic energy 133
perpetual 139
vibrations 126
motor cycles, engines 143
motors, electric 158
moulding
glass 110
plastics 101

Mount Saint Helen’s 216
Mount Semirodriki
telescope 198

Mount Wilson telescope 198
mountains (ecology) 384
air pressure 127, 250
avalanches 266
building 210, 214, 218-19
climate 244
ecosystems 371
rainfall 264
temperature 251
and weather 249
mouse, computers 173
movement, animals 356-7
see also motion
movies 208
mud pools 217
Muller, Alex 149
multimeters 152
multipole motors 158
Munsell colour tree 203

Murray, Yvonne 252
muscles 355
cellular respiration 346
electricity 151
energy 132, 133
movement 356
mushroom rocks 230
mushrooms 315
music

acoustics 184
electronic 189
sounds 186-7
musical instruments 126,
413

muskoxen 383
mussels 324
mutations, genetic 364
mutualism 379
myelin 360
mylonite 224
myofibrils 355
myths, creation of the
Earth 209

nail varnish 103
names

chemicals 404
living things 310-11
naphtha 98, 406
Napoleon I, Emperor 63,
270

Napoleon III, Emperor 87
natural gas 97, 239
see also gas

natural selection 309, 380
navigation
compasses 154
maps 209
migration 381
stars 282
nebulae 274, 276
nectar 342, 380
nematocysts 320
nematodes 321, 421
neon 48, 193
Neptune 283, 293
discovery of 292
space probes 273, 293,
301

statistics 418
Nereid 293
nerves 360
nervous system
brain 361

internal environment 350
muscles 355
salts 73

nests, birds 333
neurons 24-5, 360-1
neutralization 71
neutron stars 22,281
Newcomen, Thomas 144
Newton, Sir Isaac 120, 123
theory of gravity 283
theory of light 190
newtonometers 123
newtons 123
Newton’s cradle 139
newts 328, 329
niches, ecosystems 370
nickel 36, 37
nickel cadmium cells 150
Niepce, Joseph Nicephore
206, 207
night vision 205
Nile, River 388
nimbostratus clouds 261,
264

Nipkow, Paul 167
nitrates 373
nitric acid 68, 90
nitrogen 42

in air 74
ammonia 90
bonds 29
fertilizers 90
nitrogen cycle 373
nitrogen dioxide 54
nitroglycerine 42
noble gases 48
nocturnal animals 391
nodes, harmonics 186
noise, loudness 181
see also sound
non-contact forces 115
non-destructive testing
(NDT) 185
non-living matter 17
Norse gods 257
North America
continental drift 215
droughts 242, 265
Ice Age 246
temperate forests 396
North Pole
ecology 382
magnetic field 213
seasons 211
temperature 251
north pole, magnetism 154,
155

North Star 282
Northern Hemisphere
hurricanes 258
seasons 211,243
stars 419

northern lights 154, 213
Norway, fjords 236
NOT gates, logic circuits
171

nuclear energy 113, 136-7
pollution 373, 383
radioactivity 27
waste products 136
nuclear fission 136
nuclear forces 115
nuclear fusion 136
source of energy 137
stars 137,278,280
in the Sun 47, 137,284
nuclear weapons 113,137
nucleus
atoms 24-5
cells 337, 338
nuee ardente 216
numbers

binary system 172 ,411
decimal system 411
nunataks 229
nutrient cycle 393
nutrition 342
nylon 100, 107

oak trees 396
oases 391
observatories 297
occluded fronts 253,270
oceanic crust 210
oceans 234-7
currents 244
(ecology) 371, 386-7
hurricanes 258
plankton 306
pollution 387
seafloor spreading 214-15
sedimentary rocks 223
shorelines 236-7
tides 122
waterspouts 259
waves, tides and currents
235

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Texts

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "The Dorling Kindersley Science Encyclopedia"

See other formats